Chemistry By Jocelyn Ventura
Multiple choice
Questions and Answers
- 1.
A glowing match was dropped into a dry gas jar containing one gas only. The match (but not the gas) caught a light. Which gas is most likely present in the jar?
- A.
A. oxygen
- B.
B. hydrogen
- C.
C. Carbon dioxide
- D.
D. Carbon monoxide
Correct Answer
A. A. oxygenExplanation
Oxygen is most likely present in the jar because it supports combustion and allows the match to catch fire. Hydrogen, carbon dioxide, and carbon monoxide do not support combustion, so they would not cause the match to catch fire.Rate this question:
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- 2.
Which statement does NOT correctly describe a salt?
- A.
A. It is a compound
- B.
B. It is a pure substance
- C.
C. It always contains oxygen
- D.
D. It is a chemical combination of a metal and a non-metal
Correct Answer
C. C. It always contains oxygenExplanation
Salt is a compound that is formed when a metal and a non-metal combine chemically. It is a pure substance because it is made up of only one type of molecule. However, not all salts contain oxygen. Some salts, such as sodium chloride (table salt), do not contain oxygen. Therefore, statement C is incorrect.Rate this question:
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- 3.
Which information gives the composition of a compound?
- A.
A. kind of element present
- B.
B. kind and amount of element present
- C.
C. kind and volume of elements present
- D.
D. amount and volume of the elements present
Correct Answer
B. B. kind and amount of element presentExplanation
The correct answer is B. kind and amount of element present. This is because the composition of a compound refers to the types of elements present in the compound and the ratio of these elements. The amount of each element present in the compound is also important in determining its composition. Therefore, both the kind and amount of elements present are necessary to fully describe the composition of a compound.Rate this question:
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- 4.
Which statement correctly distinguishes between an element and a compound?
- A.
A. An element is homogeneous while a compound is a heterogeneous.
- B.
B. An element has a sharp melting point while a compound melts over a temperature range.
- C.
C. An element gains mass when heated in the presence of air while a compound loses mass when heated in the presence of air.
- D.
D. An element is a one phase system while a compound is a two phase system.
Correct Answer
C. C. An element gains mass when heated in the presence of air while a compound loses mass when heated in the presence of air.Explanation
An element is a pure substance that cannot be broken down into simpler substances by chemical means. When heated in the presence of air, some elements can react with oxygen and gain mass, such as iron rusting. On the other hand, a compound is a substance composed of two or more elements chemically combined. When heated in the presence of air, some compounds can decompose and lose mass, such as water evaporating into steam. Therefore, the statement that an element gains mass when heated in the presence of air while a compound loses mass when heated in the presence of air correctly distinguishes between an element and a compound.Rate this question:
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- 5.
To which does the law of definite composition apply?
- A.
A. a sample of ice
- B.
B. a pure sample of copper
- C.
C. a solution of salt in water
- D.
D. a mixture of oxygen gas and nitrogen gas
Correct Answer
A. A. a sample of iceExplanation
The law of definite composition applies to a sample of ice. This law states that a compound is always composed of the same elements in the same proportions by mass. Ice is a compound made up of water molecules, which always have the same ratio of hydrogen to oxygen atoms. Therefore, the composition of ice is definite and follows the law of definite composition.Rate this question:
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- 6.
A clear, colorless liquid boils sharply at 80.1 ÌŠC. It is soluble in alcohol. It burns when ignited. Analysis shows it has a definite composition: 92% carbon and 8% hydrogen by mass. Which properties of the liquid show it is a compound, NOT a mixture?
- A.
A. It is a liquid and burns
- B.
B. it is clear and colorless
- C.
C. it is soluble in alcohol and burns
- D.
D. It boils sharply and has a definite composition
Correct Answer
D. D. It boils sharply and has a definite compositionExplanation
The properties of the liquid that show it is a compound, not a mixture, are that it boils sharply and has a definite composition. Boiling sharply indicates that the liquid has a specific boiling point, which is characteristic of compounds rather than mixtures. Additionally, the fact that the liquid has a definite composition of 92% carbon and 8% hydrogen by mass further suggests that it is a compound with a fixed ratio of elements.Rate this question:
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- 7.
Which property of water do you expect NOT to change when salt is added to it?
- A.
A. its density
- B.
B. its freezing point
- C.
C. its boiling point
- D.
D. its non flammability
Correct Answer
D. D. its non flammabilityExplanation
When salt is added to water, the property that is not expected to change is its non flammability. Adding salt to water does not affect its ability to extinguish fires or its resistance to burning.Rate this question:
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- 8.
. Calcium combines with sulfur in a mass ratio of 5:4. If 10g each of Calcium and Sulfur are mixed and heat is applied in a closed vessel, what will remain unreacted after the reaction?
- A.
A. 6 g Sulfur
- B.
B. 2 g Sulfur
- C.
C. 2 g Calcium
- D.
D. 6 g Calcium
Correct Answer
B. B. 2 g SulfurExplanation
When calcium and sulfur react, they combine in a mass ratio of 5:4. This means that for every 5 grams of calcium, 4 grams of sulfur are needed for a complete reaction. In this scenario, 10 grams each of calcium and sulfur are mixed. Since the ratio of calcium to sulfur is 5:4, it means that 8 grams of sulfur will react with all 10 grams of calcium. Therefore, 2 grams of sulfur will remain unreacted after the reaction.Rate this question:
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- 9.
Elements A and B reacted to form compound AB. The data obtained by four students are shown in the table. What general statement INCORRECTLY describe the data given in the table? STUDENT MASS of A (g) MASS of B (g) MASS AB (g) 1 1.0 0.5 1.5 2 1.4 0.7 2.1 3 1.8 0.9 2.7 4 2.0 1.0 3.0
- A.
A. AB has no definite composition.
- B.
B. AB is made up of two parts of A and one part B by mass.
- C.
C. The sum of the masses of A and B equals the mass of AB.
- D.
D. The elements A and B combined in definite proportion by mass in forming AB.
Correct Answer
A. A. AB has no definite composition.Explanation
The data in the table shows that the mass of compound AB varies depending on the masses of elements A and B. This indicates that the composition of AB is not constant and can vary. Therefore, option A, which states that AB has no definite composition, is the correct answer.Rate this question:
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- 10.
Which of the following should you NOT do when preparing herbal medicines from plant leaves?
- A.
A. Use aluminium pots
- B.
B. Use only fresh, clean leaves
- C.
C. store in brown-colored bottles
- D.
D. apply low heat for a longer period
Correct Answer
A. A. Use aluminium potsExplanation
Aluminium pots should not be used when preparing herbal medicines from plant leaves because aluminium can react with the compounds in the leaves and contaminate the medicine. It is recommended to use stainless steel or glass pots instead.Rate this question:
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- 11.
Two substances were made to react in a cloud vessel. Which will remain the same before and after the reaction?
- A.
A. mass of the product
- B.
B. mass of the reactants
- C.
C. temperature of the vessel.
- D.
D. total mass of reactants and products
Correct Answer
D. D. total mass of reactants and productsExplanation
The total mass of reactants and products will remain the same before and after the reaction because of the law of conservation of mass. According to this law, matter cannot be created or destroyed in a chemical reaction, only rearranged. Therefore, the total mass of the substances involved in the reaction will always remain constant.Rate this question:
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- 12.
Powdered copper when heated in an atmosphere of oxygen produces copper (II) oxide according to the chemical equation. 2Cu + Oâ‚‚ -----------> 2 Cu O What is the mass of copper (II) oxide that forms?
- A.
A. The same as the mass of copper.
- B.
B. Twice the mass of oxygen that combined with copper
- C.
C. The sum of the masses of copper and oxygen that combined.
- D.
D. The sum of twice the mass of copper and the mass of oxygen that combined.
Correct Answer
C. C. The sum of the masses of copper and oxygen that combined.Explanation
When copper reacts with oxygen to form copper (II) oxide, the mass of copper and the mass of oxygen combine to form the mass of copper (II) oxide. This is because mass is conserved in a chemical reaction, meaning that the total mass of the reactants is equal to the total mass of the products. Therefore, the mass of copper (II) oxide that forms is equal to the sum of the masses of copper and oxygen that combined.Rate this question:
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- 13.
Given the chemical equation A + B ---------->C + D. If the masses of A, B, and C are given, how do you determine the mass of D?
- A.
A. Multiply the mass of C by 2
- B.
B. Add the masses of A, B, and C.
- C.
C. Add the masses of A and B, and subtract the mass of C
- D.
D. Add the masses of A and B, and subtract from the mass of C.
Correct Answer
C. C. Add the masses of A and B, and subtract the mass of CExplanation
To determine the mass of D in the chemical equation, you need to add the masses of A and B, and then subtract the mass of C. This is because in a chemical reaction, mass is conserved. The total mass of the reactants (A and B) should be equal to the total mass of the products (C and D). Therefore, by subtracting the mass of C from the total mass of A and B, you can find the mass of D.Rate this question:
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- 14.
A weighed amount of copper was heated in the presence of air. Its color was observed to turn reddish black. On cooling, the material was weighed again. How does the mass after heating compare with the mass before heating?
- A.
A. It is greater than the mass before heating.
- B.
B. it is less than the mass before heating
- C.
C. It can not be predicted
- D.
D. They are the same.
Correct Answer
A. A. It is greater than the mass before heating.Explanation
When copper is heated in the presence of air, it undergoes oxidation and forms copper oxide, which has a reddish black color. The increase in mass after heating is due to the addition of oxygen from the air to the copper. Therefore, the mass after heating is greater than the mass before heating.Rate this question:
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- 15.
The law illustrated in item No.15 is __________________.
- A.
A. Dalton’s Law
- B.
B. law of mass Conservation
- C.
C. Law of Multiple Proportion
- D.
D. law of Definite Composition
Correct Answer
B. B. law of mass ConservationExplanation
The correct answer is the law of mass conservation because this law states that in a chemical reaction, matter cannot be created or destroyed, it can only be rearranged. This means that the total mass of the reactants must be equal to the total mass of the products.Rate this question:
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- 16.
In the reaction: A + B--------> C, 10g of A reacted with B to produce 25 g of C. the mass of B that reacted is ____________.
- A.
A. 10 g
- B.
B. 15 g
- C.
C. 25 g
- D.
D. 35 g
Correct Answer
B. B. 15 gExplanation
According to the law of conservation of mass, the total mass of the reactants must be equal to the total mass of the products. In this reaction, 10g of A reacted with B to produce 25g of C. Therefore, the mass of B that reacted can be calculated by subtracting the mass of A from the total mass of the products: 25g - 10g = 15g. So, the correct answer is B. 15g.Rate this question:
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- 17.
What is conserved in a chemical reaction?
- A.
A. Number of molecules of reactants
- B.
B. Chemical composition
- C.
C. Volume
- D.
D. mass
Correct Answer
D. D. massExplanation
In a chemical reaction, the total mass of the reactants is equal to the total mass of the products. This is known as the law of conservation of mass. This means that even though the reactants may undergo a chemical change and rearrange their atoms to form new products, the total mass of the system remains constant. Therefore, the correct answer is D. mass.Rate this question:
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- 18.
Analysis shows ammonia to contain 14 g of nitrogen for every 3.0 g of hydrogen. How many grams of nitrogen are needed to react with 0.15 g hydrogen to produce ammonia?
- A.
A. 0.30 g
- B.
B. 0.50 g
- C.
C. 0.70 g
- D.
D. 0.90 g
Correct Answer
C. C. 0.70 gExplanation
Based on the given information, we know that for every 3.0 g of hydrogen, there are 14 g of nitrogen in ammonia. Therefore, we can set up a proportion to find the amount of nitrogen needed to react with 0.15 g of hydrogen.
(14 g of nitrogen / 3.0 g of hydrogen) = (x g of nitrogen / 0.15 g of hydrogen)
Cross-multiplying and solving for x, we get:
x = (14 g of nitrogen / 3.0 g of hydrogen) * 0.15 g of hydrogen
x = 0.7 g of nitrogen
Therefore, the correct answer is C. 0.70 g.Rate this question:
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- 19.
Why can’t you change the formula of a compound in order to balance a reaction?
- A.
A. The elements that combine have definite composition and fixed proportion of elements by mass.
- B.
B. The number of atoms in the left should be equal to the atoms on the right of the arrow.
- C.
C. The elements have definite mass ratios.
- D.
D. The molecules are indestructible.
Correct Answer
A. A. The elements that combine have definite composition and fixed proportion of elements by mass.Explanation
The correct answer is A because compounds have a fixed ratio of elements by mass. Changing the formula of a compound would change the ratio of elements, which would result in a different compound and therefore a different reaction.Rate this question:
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- 20.
Exactly 24 g of a silvery white substances was completely burned in an open vessel. A grey ash was formed. The ash was found to be 40 g. What does this indicate?
- A.
A. The substance combined with another element to form a compound.
- B.
B. The substance decomposed and became ash after burning.
- C.
C. The substance is a compound.
- D.
D. The substance is impure.
Correct Answer
A. A. The substance combined with another element to form a compound.Explanation
The formation of ash after burning indicates that the substance combined with another element to form a compound.Rate this question:
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- 21.
. Consider the following reactions: a. White crystal ---------> black solid + colorless gas b. Very dark violet crystal ------------> violet gas ------------> fine violet crystals c. Red powder ----------> Silvery liquid + colorless gas Which reactant is an element?
- A.
A. the white crystal
- B.
B. the dark violet crystal
- C.
C. the red powder
- D.
D. white crystal and red powder
Correct Answer
B. B. the dark violet crystalExplanation
The dark violet crystal is an element because it undergoes a reaction where it transforms into a violet gas and then forms fine violet crystals. This indicates that the dark violet crystal is a pure substance that cannot be further broken down into simpler substances, which is a characteristic of an element.Rate this question:
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- 22.
Which carries the current in an electrolytic conductor?
- A.
A. molecules
- B.
B. electrons
- C.
C. atoms
- D.
D. ions
Correct Answer
D. D. ionsExplanation
In an electrolytic conductor, the current is carried by ions. In an electrolyte solution, the molecules of the solute dissociate into ions, which are then able to move and carry electric charge. These ions can be positively charged (cations) or negatively charged (anions), and they are responsible for conducting the current in the electrolyte. Therefore, the correct answer is D. ions.Rate this question:
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- 23.
Dalton’s Atomic Theory explains the laws of chemical changes. Which of Dalton’s assumptions explains the Law of Conservation of Mass?
- A.
A. An atom is the smallest particle of an element.
- B.
B. Atoms combine in ratios of small whole numbers.
- C.
C. Atoms of a given element have the same properties of size, shape and mass.
- D.
D. In an ordinary chemical reactions, no new atoms are created and no old ones are destroyed.
Correct Answer
D. D. In an ordinary chemical reactions, no new atoms are created and no old ones are destroyed.Explanation
Dalton's Atomic Theory states that in an ordinary chemical reaction, no new atoms are created and no old ones are destroyed. This assumption explains the Law of Conservation of Mass, which states that the total mass of the reactants in a chemical reaction is equal to the total mass of the products. This means that the mass of the substances involved in a chemical reaction remains constant, supporting the idea that atoms are not created or destroyed during the reaction.Rate this question:
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- 24.
Calcium combines with sulfur in a mass ratio of 5:4. If 10 g each of Calcium and sulfur are mixed and heat is applied in a closed vessel, a) What will remain unreacted after the reaction?
- A.
A. 2 g Sulfur
- B.
B. 2 g Calcium
- C.
C.6 g Sulfur
- D.
D. 6 g Calcium
Correct Answer
A. A. 2 g SulfurExplanation
When calcium and sulfur react in a mass ratio of 5:4, it means that for every 5 grams of calcium, 4 grams of sulfur will react. In this case, since we have 10 grams of both calcium and sulfur, there will be an excess of sulfur.
To find out how much sulfur will remain unreacted, we can set up a proportion:
5 grams of calcium reacts with 4 grams of sulfur
10 grams of calcium reacts with x grams of sulfur (x represents the amount of sulfur that will react)
By cross multiplying, we get:
5 * x = 10 * 4
x = 20 grams of sulfur will react
Since we initially had 10 grams of sulfur, and 20 grams will react, 10 - 20 = -10 grams of sulfur will remain unreacted. However, it is not possible to have a negative mass, so the correct answer is that no sulfur will remain unreacted.Rate this question:
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- 25.
. Calcium combines with sulfur in a mass ratio of 5:4. If 10 g each of Calcium and sulfur are mixed and heat is applied in a closed vessel. What element all consumed during the chemical reaction?
- A.
A. Sulfur
- B.
B. Calcium
- C.
C. Sulfur and Calcium
- D.
D. Calcium and Sulfide
Correct Answer
B. B. CalciumExplanation
In the given question, it is stated that calcium combines with sulfur in a mass ratio of 5:4. This means that for every 5 grams of calcium, there will be 4 grams of sulfur. If 10 grams each of calcium and sulfur are mixed and heated in a closed vessel, the calcium will completely react with the sulfur according to the given ratio. Therefore, all of the calcium will be consumed during the chemical reaction, making option B, Calcium, the correct answer.Rate this question:
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