Question 9

Question

An isotope of the element nitrogen has 7 protons and 9 neutrons. What is the name of the isotope?

a
Nitrogen-7
b
Nitrogen-9
c
Nitrogen-14
d
Nitrogen-16
Question 10
The chemical equation for the reaction between magnesium (Mg) and hydrochloric acid (HCl) is shown.

Mg + 2HCl → MgCl2 + H2

Fiona weighs the magnesium and hydrochloric acid before the reaction and finds a total mass of 55 grams. After the reaction, she measures the mass of the products, magnesium chloride (MgCl2) and hydrogen (H2), and finds a total mass of 55 grams again. Does Fiona's data support the law of conservation of matter, and why?

a
Yes, because the mass of the reactants is the same as the mass of the products in her data.
b
Yes, because the mass of the reactants is lower than the mass of the products in her data.
c
No, because the mass of the reactants is the same as the mass of the products in her data.
d
No, because the mass of the reactants is lower than the mass of the products in her data.
Question 11
Americium-241 is a radioactive substance used in smoke detectors. The half life of americium is 432 years. If a smoke detector initially contains 1 gram of Americium 241, how much will remain in 1,296 years?

a
0.5 g
b
0.125 g
c
1.0 g
d
0.25 g

Answer 1

Question 9:
The isotope of nitrogen with 7 protons and 9 neutrons has a mass number of \(7 + 9 = 16\). Therefore, the name of the isotope is:

d. Nitrogen-16

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Question 10:
According to the law of conservation of matter, the mass of the reactants must equal the mass of the products in a chemical reaction. Since Fiona measured the total mass of the reactants (55 grams) and found the total mass of the products (also 55 grams) to be the same, her data supports this law. Thus, the correct answer is:

a. Yes, because the mass of the reactants is the same as the mass of the products in her data.

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Question 11:
The half-life of americium-241 is 432 years. In 1,296 years, which is three half-lives (1,296/432 = 3), the amount remaining can be calculated as follows:

1. After the first half-life (432 years):

   • \(1 , \text{g} \rightarrow 0.5 , \text{g}\)

2. After the second half-life (864 years):

   • \(0.5 , \text{g} \rightarrow 0.25 , \text{g}\)

3. After the third half-life (1,296 years):

   • \(0.25 , \text{g} \rightarrow 0.125 , \text{g}\)

Thus, the amount of americium-241 remaining after 1,296 years is:

b. 0.125 g