Question

Please I need help on these 3 questions. Thank You.​

Answer 1

1.

V = 200 mL (volume)

c = 3 M = 3 mol/L (concentration)

First we convert mL to L:

200 mL = 0.2 L

Then we calculate the moles using the formula: n = V × c = 0.2 L × 3 mol = 0.6 mol

Finally, we just use the molar mass of CaF2 to calculate the actual mass:

molar mass = 78 g/mol

The formula is: m = n × mm (mass = moles × molar mass)

m = 0.6 mol × 78 g/mol = 46.8 g

2.

For this question the steps are exactly like the first question.

V = 50mL = 0.05 L

c = 12 M = 12 mol/L

n = V × c = 0.05 L × 12 mol/L = 0.6 mol

molar mass (HCl) = 36.5 g/mol

m = n × mm = 0.6 mol × 36.5 g/mol = 21.9 g.

3.

The steps for this question are the opposite way.

m(K2CO3) = 250 g

molar mass = 138 g/mol

n = m ÷ mm = 1.81 mol

c = 2 mol/L

V = n ÷ c = 1.81 mol ÷ 2 mol/L = 0.905 L = 905 mL