Grade 10 Academic Science - Chemistry Question 1. What is the electron configuration of the element calcium (Ca)?

Grade 10 Academic Science - Chemistry Answer 1. The correct electron configuration is 2,8,8,2. This configuration means that the calcium element has four electron shells. There are two electrons in Shell #1, eight electrons in Shell #2 and Shell #3, and two electrons in Shell #4. To reach a stable electron configuration, the calcium ion would give away the two valence electrons in Shell #4. The ionic charge would be 2+. Why? The calcium ion has 20+ protons and 18- electrons. Two extra positive-charge protons means ionic charge 2+.

Grade 10 Academic Science - Chemistry Question 2. A bond forms between two non-metals. For this bond to occur, the two atoms must share electrons. These characteristics describe which type of bond?

Grade 10 Academic Science - Chemistry Answer 2. The type of bond that occurs between non-metals that share electrons is a COVALENT BOND. The metals both have a negative charge. Similar charges should repel, but these atoms attract. To do so, the electronegativity of each element (i.e., the ability to attract electrons) is nearly equal. Neither element has a stronger ability to pull (attract) electrons. Thus, the non-metals share.

Grade 10 Academic Science - Chemistry Question 3. What TYPE of chemical reaction is shown in the following formula? 2HNO3 + CaCl2 2HCl + Ca(NO3)2

Grade 10 Academic Science - Chemistry Answer 3. 2HNO3 + CaCl2 2HCl + Ca(NO3)2 This is a Double Displacement Reaction Recall the General Formula: AB + CD AD + CB There are four different elements / compounds (H, NO3, Ca and Cl). In this reaction, they change places and two new compounds form as products. Thus, this is Double Displacement.

Grade 10 Academic Science - Chemistry Question 4. A chemical reaction has reactants and products. What are the products in the following combustion reaction? CH4 + 2O2 CO2 + 2H2O

Grade 10 Academic Science - Chemistry Answer 4. As in all combustion reactions, the products are carbon dioxide (CO2) and water (H2O). The products of a chemical reaction are the outcomes of the change. The products will always be listed on the “right side” of the chemical equation.

Grade 10 Academic Science - Chemistry Question 5. Sodium and oxygen are mixed in a chemical reaction. Sodium oxide forms. Balance the chemical equation for this reaction ___ Na + _____O2 ______ Na2O

Grade 10 Academic Science - Chemistry Answer 5. 4Na + O2 2Na2O The chemical formula indicates that you must add four atoms of sodium to one atom of oxygen gas to produce two atoms of sodium oxide. 4Na means four atoms of sodium 2Na2O is 2X2 or four atoms of sodium + 2X1 or two atoms of oxygen. There are equal amounts of all elements on both sides of the equation. The Law of Conservation of Mass is met (Reactants = Products). Thus, the equation is balanced.

Grade 10 Academic Science - Chemistry Question 6. You have some calcium hydroxide. The chemical formula is Ca(OH)2. Do you have an acid or a base?

Grade 10 Academic Science - Chemistry Answer 6. Ca(OH)2 is a base. Another name is alkaline, A base has the following properties: pH > 7 in an aqueous solution Dissolves in water Conducts electricity Tastes bitter Feels slippery Turns red litmus paper blue Do not react with metals Can burn skin (corrosive) Reacts with acids to neutralize the acid

Grade 10 Academic Science - Chemistry Question 7. In the following reaction CH4 + 2O2 CO2 + 2H2O you would need two moles of oxygen to burn all the carbon in one mole of methane. In other words, you need 32g O2 for every 16g CH4. If you have less than 32g O2, what type of reaction occurs?

Grade 10 Academic Science - Chemistry Answer 7. The question refers to “burning.” Thus, this is a combustion reaction. Yet, there is not enough oxygen to combust (i.e., burn) all the carbon. There is carbon remaining. This is an Incomplete Combustion Reaction. The remaining carbon forms carbon monoxide (CO). It is a colourless, odourless and toxic gas. Also, soot is produced as a by-product of incomplete combustion.

Grade 10 Academic Science - Chemistry Question 8. How many valence electrons occur in the chlorine element?

Grade 10 Academic Science - Chemistry Answer 8. Chlorine has seven valence electrons. The valence electrons are the electrons that reside in the outer shell of electrons. Chlorine is Element #17. It has three electrons shells. There are two electrons in Shell #1, eight electrons in Shell #2 and seven electrons in Shell #3. In this case, Shell #3 holds the valence electrons. Thus, there are seven valence electrons in the chlorine element.

Grade 10 Academic Science - Chemistry Question 9. What is the chemical formula for manganese (IV) oxide?

Grade 10 Academic Science - Chemistry Answer 9. The formula for manganese (IV) oxide is MgO2. According to the Periodic Table, manganese (Mn #25) has two possible ionic charges: 2+ and 4+. The Roman Numeral tells you to use 4+ or Mn4+. So, you are bonding Mn4+ with O2- (see the Periodic Table for the ionic charge of oxygen). That should produce Mn2O4. Wait, you can reduce because 4 and 2 are divisive. Thus, MnO2 is the correct chemical formula.

Grade 10 Academic Science - Chemistry Question 10. You have a compound with the following characteristics: At room temperature, it is a brittle solid that can be crushed It has a crystal shape with an alternating arrangement of positively-charged ions and negatively-charged ions It has a high melting point When dissolved in water, the crystal structure breaks down. To form, electrons are transferred from the positive ion to the negative ion. What type of compound do you have?

Grade 10 Academic Science - Chemistry Answer 10. These properties describe an Ionic Compound. An Ionic Compound is a metal bonding with a non-metal.

Grade 10 Academic Science - Chemistry Question 11. What is the chemical formula for diphosphorus pentoxide?

Grade 10 Academic Science - Chemistry Answer 11. The chemical formula is P2O5. Each component of the compound has a prefix: diphosphorus and pentoxide. In chemistry, di = 2 and penta =5. The prefix indicates the number of each component. This diphosphorus is P2 or two atoms of phosphorus. Pentoxide is O5 or five atoms of oxygen. Thus P2O5 is a molecular compound (bonding of two non-metals).

Grade 10 Academic Science - Chemistry Question 12. Sodium sulfate is mixed with iron (II) chloride. They react to produce sodium chloride and iron (II) sulfate. Write and balance the chemical formula for the reaction.

Grade 10 Academic Science - Chemistry Answer 12. The skeleton chemical formula is Na2SO4 + FeCl2 NaCl + FeSO4 Why FeCl2? Iron has two possible ionic charges (2+ and 3+). Iron (II) chloride tells you to use the 2+ charge. Since Cl is 1-, it is Fe2+ + Cl1- to give FeCl2 Why Na2SO4? SO4 is sulfate….a polyatomic. It is treated as one and SO4 has an ionic charge of 2-. Thus Na1+ + (SO4)2- is Na2SO4 Now balance the formula. The Law of Conservation of Mass states mass of reactants = mass of products. Na2SO4 + FeCl2 2NaCl + FeSO4