Consider a solution which is 0.15 M in HF and 0.10 M in KF. Which response contains all the true statements, and no others?

I. If NaOH is added, potassium ion reacts with hydroxide ion.
II. If a small amount of NaOH is added, the pH increases very slightly.
III. If HNO3 is added, hydrogen ion reacts with fluoride ion.
IV. If more KF is added, the pH decreases.

A. I, III, and IV
B. II and III
C. II and IV
D. III
E. another combination.

B. II and III

Explanation:

I. If NaOH is added, potassium ion reacts with hydroxide ion. False

II. If a small amount of NaOH is added, the pH increases very slightly. True

III. If HNO3 is added, hydrogen ion reacts with fluoride ion. True

IV. If more KF is added, the pH decreases. False

Based on the above option B is the only response that contains all the true statements because when a small amount of NaOH is added to the solution, the pH increases very slightly and if more nitric acid (HNO3) is added, since nitric acid is a strong acid that is stronger than HF, the nitric acid (HNO3) will protonate.

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"