Answered

1
Which equation represents a chemical change?
A BaCl2(s) → BaCl2(1)
B Ca2+ (aq) + SO4(aq) → CaSO4(s)
C KCI(s) + H2O(1) →> K(aq) Cl(aq)
D Na (aq) + NO3(aq) → NaNO3(aq)
2
Which sample contains the largest number of molecules?
A
16g of methane, CH4(g)
B
16g of oxygen, O2(g)
C 16g of phosphorus, P4(s)
D
16 dm³ of methane at r.t.p., CH4(g)
3
Lead(II) sulfate is an insoluble salt.
Which reaction produces a mixture from which lead(II) sulfate is obtained by filtration?
A adding solid lead(II) carbonate to dilute sulfuric acid
B adding solid lead(II) hydroxide to dilute sulfuric acid
C adding metallic lead to dilute sulfuric acid
D adding aqueous lead(II) nitrate to dilute sulfuric acid



Answer :

GinnyAnswer
1. The equation that represents a chemical change is option B: Ca2+ (aq) + SO4(aq) → CaSO4(s). In this equation, two aqueous substances (Ca2+ and SO4) react to form a solid precipitate (CaSO4), indicating a chemical change where new substances are formed. 2. The sample that contains the largest number of molecules is option B: 16g of oxygen, O2(g). This is because oxygen exists as O2 molecules, which are diatomic (composed of two oxygen atoms), while methane (CH4) and phosphorus (P4) exist as individual molecules. Therefore, for the same mass, oxygen molecules have a higher count compared to individual methane or phosphorus molecules. 3. The reaction that produces a mixture from which lead(II) sulfate is obtained by filtration is option A: adding solid lead(II) carbonate to dilute sulfuric acid. When lead(II) carbonate reacts with sulfuric acid, it forms lead(II) sulfate, which is insoluble and can be filtered out from the mixture. The other options do not lead to the formation of lead(II) sulfate through a filtration process, making option A the correct choice for obtaining lead(II) sulfate.

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