Chemistry Practice Test, Che102 Practice Final Exam

Hard water contains ions like calcium, magnesium, and iron. These ions are present in the water due to the dissolution of minerals such as calcium carbonate, magnesium sulfate, and iron oxide. When water comes into contact with rocks and soil containing these minerals, it picks up the ions and becomes hard water. These ions can cause various issues such as scale buildup in pipes and appliances, reduced effectiveness of soaps and detergents, and can even affect the taste and appearance of water.

Enzymes in saliva are responsible for breaking down starch in food. Saliva contains an enzyme called amylase, which specifically targets and breaks down the complex carbohydrates present in starch. This process starts in the mouth, where the food is mixed with saliva through chewing and begins to break down the starch into simpler sugars. These simpler sugars can then be further digested and absorbed by the body.

Alkenes contain at least one double bond, which is the key difference between alkenes and alkanes. Alkanes, on the other hand, do not contain any double bonds. The presence of a double bond in alkenes gives them different chemical and physical properties compared to alkanes. Alkenes are generally more reactive than alkanes due to the presence of the double bond, which allows them to undergo addition reactions. In contrast, alkanes are relatively unreactive due to the absence of double bonds.

The black balls in the model kits used to represent organic molecules have four holes because they represent carbon, which makes four bonds. Carbon is a versatile element in organic chemistry and can form stable covalent bonds with up to four other atoms. The four holes in the black balls allow for the attachment of other atoms or molecules, representing the bonds formed by carbon in organic compounds.

Oxygen in organic compounds typically forms two bonds. This is because oxygen has six valence electrons and needs two more electrons to achieve a stable octet configuration. By forming two bonds, oxygen can share electrons with other atoms and fulfill its electron requirement. This allows oxygen to participate in various chemical reactions and contribute to the structure and properties of organic compounds.

Casein is an important protein in milk because it is responsible for the white color and the majority of the nutritional value of milk. It is a complete protein, meaning it contains all the essential amino acids necessary for human growth and development. Casein also plays a crucial role in the formation and stabilization of milk curds, which are used in the production of cheese and other dairy products.

Sucrose and lactose are disaccharides because they are composed of two monosaccharide units. Sucrose is made up of glucose and fructose, while lactose is made up of glucose and galactose. Disaccharides are formed through a condensation reaction where a molecule of water is removed, resulting in the formation of a glycosidic bond between the two monosaccharides.

When an alkene reacts with bromine, the type of reaction occurring is called addition. This is because the bromine molecule adds across the double bond of the alkene, resulting in the formation of a bromoalkane. This type of reaction is characteristic of alkenes and is known as an addition reaction. Combustion involves the reaction of a substance with oxygen to produce heat and light, hydrolysis involves the reaction of a compound with water to break it down, and neutralization involves the reaction of an acid with a base to form a salt and water.

Proteins can be denatured by heat, acid, and heavy metals. Denaturation is a process in which the protein loses its structure and function due to external factors. Heat can break the weak bonds that hold the protein's structure together, causing it to unfold. Acidic conditions can alter the charges on the protein's surface, disrupting its interactions. Heavy metals can bind to the protein, causing conformational changes. Therefore, all of these factors can lead to protein denaturation.

In organic compounds, hydrogen typically forms one bond. This is because hydrogen has only one electron in its outer shell, and it needs to gain one more electron to achieve a stable configuration. By forming one bond, hydrogen can share its electron with another atom and achieve a stable state. This is commonly seen in organic compounds where hydrogen is often bonded to carbon, forming a single covalent bond.

Sucrose is a disaccharide composed of glucose and fructose. Hydrolysis of sucrose breaks it down into its monosaccharide components. Benedict's test is used to detect the presence of reducing sugars, such as glucose and fructose. A positive Benedict's test indicates the presence of reducing sugars, confirming that sucrose has been hydrolyzed and its monosaccharide components are present. Therefore, the hydrolysis product giving a positive Benedict's test is a clear indication that sucrose has undergone hydrolysis.

When benzamide is hydrolyzed under basic conditions, it undergoes a reaction called hydrolysis where it reacts with water molecules and breaks down. In this reaction, one of the products formed is ammonia. Therefore, when the hydrolysis of benzamide is complete, it will smell like ammonia.

The reaction described involves the combination of acetic acid and methanol to form methyl acetate. This process is known as esterification. Esterification is a type of reaction in which an alcohol and an acid combine to form an ester, with the elimination of water. In this case, acetic acid acts as the acid and methanol acts as the alcohol, resulting in the formation of methyl acetate.

An esterification reaction between glycerol and a fatty carboxylic acid produces a triglyceride. This is because glycerol, which is a type of alcohol, reacts with the carboxylic acid to form an ester bond. In the case of a fatty carboxylic acid, three ester bonds are formed with the three hydroxyl groups of glycerol, resulting in the formation of a triglyceride. A triglyceride is a type of lipid molecule that is commonly found in fats and oils.

All of the above options explain why ammonia is water soluble and N,N-dimethylaniline is not. N,N-dimethylaniline is a large non-polar molecule, which makes it less likely to dissolve in water. On the other hand, ammonia is small in size, which increases its solubility in water. Additionally, ammonia can form strong hydrogen bonds with water molecules, further enhancing its solubility. Therefore, all of these factors contribute to ammonia's water solubility compared to N,N-dimethylaniline.

At the isoelectric point, the net charge of amino acids is zero. This is because the isoelectric point is the pH at which the amino acid exists as a zwitterion, which is a molecule with both a positive and a negative charge. At this pH, the positive and negative charges cancel each other out, resulting in a net charge of zero.

The Biuret test is a chemical test used to detect the presence of proteins. It involves adding a solution of copper sulfate to the sample, followed by the addition of sodium hydroxide. If proteins are present, a color change from blue to purple will occur. Albumin, casein, and gelatin are all proteins, so they would all give a positive result in the Biuret test. Therefore, the correct answer is "all of the above".

The Lucas test would be the most helpful in identifying a 3o alcohol. The Lucas test is used to differentiate between primary, secondary, and tertiary alcohols based on their reactivity with Lucas reagent (a mixture of concentrated hydrochloric acid and zinc chloride). In this test, a tertiary alcohol reacts quickly to form a cloudy solution due to the formation of an alkyl chloride. On the other hand, primary and secondary alcohols react slowly or not at all, leading to a clear solution. Therefore, by observing the reaction rate, the student can determine if the alcohol is tertiary or not.

Stearic acid is commonly used in the preparation of skin creams as an emulsifier and stabilizer. It helps to maintain the pH balance of the cream, ensuring that it is neither too acidic nor too alkaline. This is important because the skin has a slightly acidic pH, and using a cream with a similar pH can help maintain the skin's natural barrier function and prevent irritation. Therefore, stearic acid's function in skin cream is to balance the pH.

The hydrolysis of starch was more efficient in a neutral solution because starch is a polysaccharide composed of glucose units linked by glycosidic bonds. In an acidic solution, the hydrogen ions would break these bonds, resulting in the breakdown of starch into glucose molecules. However, in a neutral solution, the hydrolysis of starch is slower as there are no excess hydrogen ions to catalyze the reaction. In a basic solution, the presence of hydroxide ions can also hinder the hydrolysis process. Therefore, a neutral solution provides the optimal conditions for efficient hydrolysis of starch.

Combustion is the best test to differentiate between an alkane and an aromatic hydrocarbon because alkanes undergo complete combustion, producing carbon dioxide and water as the only products. On the other hand, aromatic hydrocarbons can undergo incomplete combustion, resulting in the formation of carbon monoxide and soot. Therefore, if a hydrocarbon undergoes complete combustion, it is likely an alkane, whereas if it undergoes incomplete combustion, it is likely an aromatic hydrocarbon.

Chromic Acid is an oxidizing agent because it has the ability to accept electrons from other substances and cause them to undergo oxidation. It can oxidize various organic and inorganic compounds by transferring oxygen atoms or accepting electrons, resulting in the reduction of chromium in the acid. This property makes chromic acid useful in various chemical reactions, such as the oxidation of alcohols to aldehydes or ketones.

Starch is a complex carbohydrate that is broken down into glucose. It is composed of multiple glucose molecules bonded together, making it a polysaccharide. Through the process of digestion, enzymes break down the bonds between glucose molecules, allowing for the release and absorption of glucose into the bloodstream.

The percent yield is calculated by dividing the actual yield (1.75 g of aspirin) by the theoretical yield (calculated based on the starting amount of salicylic acid) and multiplying by 100. In this case, the theoretical yield can be calculated by converting the amount of salicylic acid to moles (2.00 g / 138 g/mol) and then using the mole ratio between salicylic acid and aspirin (1 mol salicylic acid produces 1 mol aspirin). The theoretical yield is therefore 2.00 g / 138 g/mol * 180 g/mol = 2.61 g. Dividing the actual yield (1.75 g) by the theoretical yield (2.61 g) and multiplying by 100 gives a percent yield of 67.1%.

The calculated percent of soy protein in soymilk would be too low because not all the protein was removed from the flask onto the cheesecloth. This means that some of the protein was left behind in the flask, resulting in a lower percentage of soy protein in the final product.

When a skin cream lacks an emulsifying ingredient, it means that there is nothing present to help the water-based and oil-based ingredients combine. As a result, the two types of ingredients will not mix properly, leading to an inconsistent texture and appearance of the cream. This can make it difficult to apply and may affect its effectiveness.

Histidine is an amino acid with a side chain that contains an imidazole ring. In its basic form, the side chain of histidine is not charged. The imidazole ring has a pKa value close to neutrality, meaning it can act as both a proton donor and acceptor depending on the pH of the environment. At physiological pH, histidine is mostly uncharged and can participate in various biochemical reactions due to its ability to donate or accept protons.

Both hexane and toluene are non-polar solvents, while water is a polar solvent. Non-polar solvents are generally not soluble in polar solvents. Therefore, neither hexane nor toluene would be expected to be soluble in water.

Soap is a mixture of sodium salts of fatty acids because when fats or oils are hydrolyzed with sodium hydroxide (NaOH), they break down into glycerol and fatty acids. The fatty acids then react with the sodium hydroxide to form sodium salts of fatty acids, which are the main components of soap. These sodium salts have the ability to dissolve in water and form micelles, which help to remove dirt and oil from surfaces when used for cleaning.

Iron (III) chloride is a commonly used reagent to test for the presence of phenol. When phenol reacts with iron (III) chloride, it forms a complex compound that has a purple color. This color change is used as a qualitative test to identify the presence of phenol in a given sample. Therefore, when iron (III) chloride is added to the mixture, it will only produce a purple color if phenol is present.

The Lucas test is used to distinguish between primary, secondary, and tertiary alcohols. In this test, the alcohol is mixed with Lucas reagent (a solution of zinc chloride in concentrated hydrochloric acid). If cloudiness or turbidity is observed immediately, it indicates the presence of a tertiary alcohol. Among the given options, tertiary butanol is the only tertiary alcohol, so it is the correct answer.

When an ester is exposed to heat under basic conditions, saponification will occur. Saponification is a chemical reaction where an ester reacts with a strong base to form a carboxylic acid salt (soap) and an alcohol. This reaction is commonly used in the production of soap. The heat and basic conditions provide the necessary conditions for the ester to break down and form the soap and alcohol.

The Ninhydrin test is positive for amino acids because it specifically reacts with the primary amino group (-NH2) present in the amino acid structure. When Ninhydrin is added to a solution containing amino acids, it forms a purple color complex, known as Ruhemann's purple. This color change is used as a qualitative test to identify the presence of amino acids in a sample. Carboxylic acids and fatty acids do not contain the amino group required for the Ninhydrin reaction, so they would not give a positive result.

Nitrogen in organic compounds typically forms three bonds. This is because nitrogen has five valence electrons and requires three more electrons to achieve a stable octet. By forming three bonds, nitrogen can share three electrons with other atoms, satisfying its electron requirement.

Since there is no black smoke observed and nothing remaining on the watchglass after the hydrocarbon is burned, it indicates that the hydrocarbon is completely combusted. Alkanes are known to burn cleanly and produce only carbon dioxide and water vapor. Therefore, it can be concluded that the hydrocarbon in question is an alkane.

The Tollen's test is used to distinguish between aldehydes and ketones. Aldehydes react with Tollens' reagent (ammoniacal silver nitrate) to form a silver mirror, while ketones do not react. Therefore, a compound that gives a positive Tollen's test must be an aldehyde. Since the correct answer is False, it implies that the compound would not give a positive Tollen's test and is therefore not an aldehyde.

Adding hydrochloric acid can increase the solubility of large amines in water because it can protonate the amine molecules. Large amines typically have a basic nature due to the presence of lone pair electrons on the nitrogen atom. Hydrochloric acid is a strong acid that can donate a proton (H+) to the amine molecules, forming ammonium ions. These ammonium ions are more soluble in water compared to the amine molecules, thus increasing the overall solubility of the large amines in water.

In the hydrolysis of sucrose, the most effective catalyst is an acid. This is because acids can donate protons, which can break the glycosidic bond in sucrose and facilitate the breakdown of the molecule into its constituent monosaccharides, glucose, and fructose. The presence of an acid increases the rate of the hydrolysis reaction by providing a favorable environment for the reaction to occur. Water, base, and sucrose itself do not possess the same proton-donating ability as acids, making them less effective catalysts in this reaction.

The differences in the solubility properties of acetic acid and benzoic acid are primarily due to their size. Acetic acid is a smaller molecule compared to benzoic acid, which allows it to form stronger intermolecular forces with water molecules. This increased interaction leads to greater solubility of acetic acid in water. On the other hand, benzoic acid is larger in size and has a more complex structure, resulting in weaker interactions with water molecules and lower solubility.

Glycine gives a negative xanthoprotein test because it does not contain a phenyl ring. Xanthoprotein test is used to detect the presence of phenolic compounds in a substance. These compounds react with nitric acid to form a yellow color. Since glycine does not have a phenyl ring in its structure, it does not react with nitric acid to produce the yellow color, resulting in a negative test.

Benedict's reagent is used to test for the presence of reducing sugars, such as glucose. In this test, glucose is oxidized, meaning it loses electrons, while the copper ions in the reagent are reduced, meaning they gain electrons. The formation of a red precipitate indicates a positive test, indicating the reduction of copper ions. Therefore, the correct answer is "glucose is oxidized, and the copper ions are reduced."

The blue-green solution formed when the unknown liquid is tested with chromic acid suggests that the compound could be a primary alcohol. This is because primary alcohols can undergo an oxidation reaction with chromic acid, resulting in the formation of a blue-green color. Ketones and alkanes do not react with chromic acid in this manner, while tertiary alcohols do not undergo oxidation reactions easily. Therefore, the most likely compound based on the test result is a 1o alcohol.

The given organic substance gives a negative ferric chloride test, which means it does not contain a phenolic group. It gives a positive ceric nitrate test, which indicates the presence of a secondary alcohol. It also gives a positive chromic acid test, suggesting the presence of a primary or secondary alcohol. Finally, it gives a positive iodoform test, indicating the presence of a methyl group attached to a carbonyl carbon. Based on these tests, the unknown organic substance is 2-butanol, as it is a secondary alcohol with a methyl group attached to the carbonyl carbon.

The amino group in the amino acid glycine gives it a positive charge in the acidic form. The amino group contains a nitrogen atom that can accept a proton, resulting in a positive charge. This protonation of the amino group occurs in acidic conditions, where protons are available to be donated. The other groups mentioned, such as the alpha carbon atom, carboxylic acid group, and side chain, do not contribute to the positive charge in the acidic form of glycine.

The iodoform test is a chemical test used to detect the presence of a methyl ketone functional group. It involves the reaction of the compound with iodine and sodium hydroxide, resulting in the formation of yellow iodoform precipitate. 2-butanone, also known as methyl ethyl ketone, is a methyl ketone and would therefore give a positive iodoform test. 1-butanol, 3-pentanone, and toluene do not have a methyl ketone functional group and would not give a positive iodoform test.

When starch is fully hydrolyzed, it breaks down into individual glucose molecules. Iodine (I2) reacts with starch to form a blue-black complex. However, since the starch has been fully hydrolyzed, there is no starch present in the solution to react with iodine. Therefore, when iodine is added to the solution, there will be no reaction and the resulting color will be yellow.

2-butanol is the correct answer because it is an alcohol that produces a yellow precipitate in the presence of iodine when heated under basic conditions. Additionally, it gives a blue-green color in the presence of chromic acid. This reaction is specific to 2-butanol and not to the other alcohols listed as options.

The ceric nitrate test is used to identify alcohols, while the iodoform test is used to identify compounds containing a methyl ketone group. 2-butanol is an alcohol, so it would give a positive result in the ceric nitrate test. 2-butanone is a methyl ketone, so it would give a positive result in the iodoform test. Cyclohexene does not contain a functional group that would react with either test, so it would not give a positive result in either test. Therefore, using the ceric nitrate and iodoform tests would clearly identify each substance.

When triethylamine (a tertiary amine) reacts with hydrochloric acid, it forms an amine salt. This is because the amine reacts with the acid to produce a salt, which consists of a positively charged ammonium ion and a negatively charged chloride ion. The formation of an amine salt is a common reaction between amines and acids, and it is an important step in various chemical processes and reactions.

Ferric chloride is used to determine the purity of aspirin because the starting material used to produce aspirin contains a phenol group, whereas aspirin itself does not. When ferric chloride is added to a solution containing a phenol group, it forms a colored complex. Therefore, if the solution turns a characteristic color when ferric chloride is added, it indicates the presence of impurities in the aspirin sample, suggesting that it is not pure.