Question

1. Which group of elements reacts violently with water?

A. noble gases B. alkali metals C. alkaline earth metals D. halogens

2. A sample of pure lithium carbonate contains 18.8 % lithium by mass. What is the % lithium by mass in a sample of pure lithium carbonate that has twice the mass of the first sample?

A. 75.2 % B. 9.40 % C. 37.6 % D. 18.8 %

Answer 1

1. Which group of elements reacts violently with water?

A:- B. Alkali metals

Explanation:

Alkali metals are very reactive, which violently reacts with water to form strong alkalies.

2 Na + 2 H2O -------> 2 NaOH + H2

2. A sample of pure lithium carbonate contains 18.8 % lithium by mass. What is the % lithium by mass in a sample of pure lithium carbonate that has twice the mass of the first sample?

A:- D. 18.8 %

Explanation:

When the mass of sample of pure lithium carbonate that has twice the mass of the first sample, the percent of lithium in the pure sample does not change. So the answer is 18.8 %.