Year 9 Chemistry Test - Mr. Hung

Metals are shiny and good conductors of heat and electricity. This is because metals have a high density of free electrons that are able to move easily and carry heat and electricity. Additionally, the arrangement of atoms in metals allows for the reflection of light, giving them their shiny appearance. Non-metals, metalloids, and gases do not possess these properties and therefore cannot be considered as shiny and good conductors of heat and electricity.

The number of electrons in an atom is equal to the number of protons. This is because atoms are electrically neutral, meaning they have no overall charge. Protons have a positive charge, while electrons have a negative charge. In order for an atom to be neutral, the number of positive charges (protons) must be equal to the number of negative charges (electrons). Therefore, the correct answer is protons.

Rubbing alcohol is the only molecule that is in a liquid state, whereas sugar is a solid and carbon dioxide and methane are gases.

Universal indicator gives us the widest range of pH values for testing solutions. It is a mixture of several different indicators that change color at different pH levels. This allows it to cover a wide range of pH values, from acidic to alkaline. Litmus solution, iodine solution, and bromothymol blue are all single indicators that only change color at specific pH levels, limiting their range of use.

Angelo required an aqueous solution of sodium chloride. Aqueous solutions are solutions in which water is the solvent. Sodium chloride is a water-soluble compound, meaning it dissolves readily in water. Therefore, to make the solution, Angelo would need to dissolve the salt in water. Vinegar, air, and oxygen gas are not suitable solvents for sodium chloride.

In the given equation, calcium carbonate reacts with hydrochloric acid to produce calcium chloride, carbon dioxide, and water. Calcium chloride is the correct answer because it is the missing chemical in the equation.

The atomic number of an atom represents the number of protons or electrons in the atom. Protons are positively charged particles found in the nucleus of an atom, while electrons are negatively charged particles that orbit around the nucleus. The atomic number determines the identity of the element, as different elements have different numbers of protons in their atoms. Therefore, the correct answer is protons or electrons.

The key idea of the Bohr Model is that there are electrons inside the atom that orbit the nucleus. This model proposed by Niels Bohr in 1913 described the structure of an atom, suggesting that electrons exist in specific energy levels or orbits around the nucleus. This concept helped to explain the stability of atoms and the emission and absorption of light by atoms.

As you move from the left side of the periodic table to the right side, the elements become less metallic. This is because the left side of the periodic table is dominated by metals, which have properties such as luster, malleability, and the ability to conduct heat and electricity. However, as you move towards the right side, the elements become more non-metallic in nature, with properties such as being brittle, dull, and poor conductors of heat and electricity. Therefore, the correct answer is that the elements become less metallic as you move from the left side to the right side of the periodic table.

Metals have a tendency to lose electrons in order to achieve a stable electron configuration, resulting in the formation of positive ions. This is because metals typically have fewer valence electrons than non-metals, making it easier for them to lose electrons rather than gain them. The loss of electrons leads to a decrease in the negative charge, resulting in the formation of positively charged ions.

The correct answer is 6 carbon atoms, 8 hydrogen atoms, and 6 oxygen atoms. This is because the chemical formula C6H8O6 indicates that there are 6 carbon atoms, 8 hydrogen atoms, and 6 oxygen atoms in Vitamin C.

In a neutralization reaction, an acid reacts with a base to form a salt and water. This is because the hydrogen ions from the acid combine with the hydroxide ions from the base to form water, while the remaining ions from the acid and base combine to form a salt. Therefore, the correct answer is salt and water.

To calculate the number of neutrons in an atom, you need to subtract the number of protons from the atomic mass. Neutrons have no charge, so they are not accounted for in the atomic mass. Therefore, by subtracting the number of protons (which is equal to the atomic number) from the atomic mass, you can determine the number of neutrons in the atom.

Rebecca correctly concluded that Cu, Zn, and Ga belong to the same period in the periodic table. Periods in the periodic table are the horizontal rows that represent the number of electron shells an element's atoms have. Elements in the same period have the same number of electron shells, but different numbers of valence electrons and similar chemical properties. Therefore, Cu, Zn, and Ga being in the same horizontal row indicates that they have the same number of electron shells and belong to the same period.

NaHCO3 is the chemical formula for baking soda. A chemical formula represents the types and numbers of atoms in a compound. In this case, NaHCO3 indicates that baking soda is composed of one sodium (Na) atom, one hydrogen (H) atom, one carbon (C) atom, and three oxygen (O) atoms. Therefore, the best representation for baking soda is its chemical formula.

When an acid reacts with a metal, it will produce hydrogen gas. This is because acids are proton donors and when they react with metals, they donate protons to the metal, causing it to release hydrogen gas as a byproduct. This reaction is known as a single displacement reaction, where the metal displaces the hydrogen from the acid, resulting in the formation of hydrogen gas.

The correct answer is "metalloids" because the question states that the seven elements between the metal and non-metal sections of the periodic table have their own color. These elements are known as metalloids, which are a group of elements that have properties of both metals and non-metals.

Alkali metals like sodium and potassium are the most reactive metals because they have only one electron in their outermost shell. This makes them highly unstable and eager to lose that electron to achieve a stable electron configuration. As a result, they readily react with other elements, especially with non-metals, to form ionic compounds. They are highly reactive with water, oxygen, and halogens, and can even catch fire or explode when exposed to air or water. Their reactivity increases as you move down the group in the periodic table.

Ionic compounds are formed when positive metal ions attract to negative non-metal ions. This is because metals tend to lose electrons and become positively charged ions, while non-metals tend to gain electrons and become negatively charged ions. The attraction between these opposite charges results in the formation of ionic compounds.

Copper (II) sulfate has one copper atom (Cu), one sulfur atom (S), and four oxygen atoms (O). Therefore, the total number of atoms in one molecule of copper (II) sulfate is 6.

The common property for both acids and bases is that they are corrosive. Acids and bases have the ability to corrode or erode certain materials, such as metals or skin, due to their chemical reactivity. This corrosive property is a characteristic shared by both acids and bases.

The formula for a liquid at room temperature is Hg (l) because Hg represents the chemical symbol for mercury and (l) indicates that it is in the liquid state. Mercury is a metal that is liquid at room temperature, making it the correct answer.

Non-metals have a higher electronegativity, meaning they have a stronger attraction for electrons. They tend to gain electrons from other atoms to achieve a stable electron configuration, resulting in the formation of negative ions. Therefore, the correct answer is "Gain, negative".

Noble gases are uncreative, colorless, and odorless in room temperature. These gases belong to Group 18 of the periodic table and have a full set of valence electrons, making them stable and unreactive. Due to their stable electron configuration, noble gases do not readily form compounds with other elements, hence their uncreative nature. They are also colorless and odorless, making them difficult to detect without specialized equipment. Oxygen, on the other hand, is a reactive gas and is not colorless or odorless, so it does not fit the description given in the question.

When two solutions are mixed together and the container feels cold, it indicates that heat is being absorbed. This suggests that an endothermic reaction is occurring, where energy is being taken in from the surroundings. As a result, the container and its contents experience a decrease in temperature, giving the sensation of coldness.

The property of changing blue litmus to red is not a property of an alkali. Alkalis are substances that have a pH greater than 7, feel slippery to touch, and have a bitter taste. They are known for their ability to neutralize acids and turn red litmus paper blue. However, they do not change blue litmus paper to red, which is a characteristic of acids.

Vinegar is not an alkali or a base because it is an acid. It is primarily composed of acetic acid, which gives it its sour taste and acidic properties. Alkalis and bases, on the other hand, are substances that have a pH greater than 7 and can neutralize acids. Limewater, soda water, and caustic soda are all examples of alkalis or bases, as they have a pH greater than 7 and can react with acids to form salts and water.

The pH value of 3.6 indicates that the solution is acidic. A pH below 7 is considered acidic, and the lower the pH value, the stronger the acidity. Since the pH of 3.6 is relatively close to 7, it suggests that the acidity is weak. Therefore, the correct answer is "weak acidic."

Potassium hydroxide has the least amount of hydrogen ions among the given chemicals. This is because potassium hydroxide is a strong base and dissociates completely in water to release hydroxide ions (OH-), but it does not release hydrogen ions (H+). In contrast, sulphuric acid, ammonia, and water all contain hydrogen ions to varying degrees. Therefore, potassium hydroxide has the least amount of hydrogen ions.

The correct answer is polyatomic and multivalent. Polyatomic ions are groups of atoms that carry a charge, while multivalent ions are ions that can have more than one possible charge. These two types of ions are different in that polyatomic ions are formed by a group of atoms bonded together, while multivalent ions can exist in multiple forms with different charges.