Question

What mass of strontium hydroxide must be dissolved in order to prepare 2.00 L of a solution with a pH of 12.00?

Answer 1

Answer:

Explanation:

The molarity of a solution (or, more precisely, of a solute in a solution) is the number of moles

of the solute in 1 litre of the solution.

molarity = M = N.B.: n = moles (solute)

litres (solution)

n

V(L)

mass (g)

MM

(MM = molar mass ≡ MW or FW)

The equation can also be used to find n (the number of moles of solute) if M (the molarity) and

V (the volume in litres) are known, and V if n and M are known.

n = MV V =

n

M

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(a) Calculate the molarity of a solution of 0.25 mole of NaOH in 5.0 L of solution.

Solution: molarity = = 0.050 M 0.25 mole

5.0 L

(b) Calculate the molarity of a solution of 4.8 mole of HCl in 600 mL of solution. (N.B.:

Convert volume to litres) (Ans. 8.0 M)

(c) Calculate the molarity of a solution of 3.6 g of NaOH in 300 mL of solution.

Solution: 300 mL = 0.300 L MM of NaOH = 40.0 g/mole

moles NaOH = = 0.090 mole 3.6 g

40.0 g/mole

molarity = = 0.30 M 0.090 mole

0.300 L

(d) Calculate the molarity of a solution of 1.25 g of Na2CO3 in 75.0 mL of solution.

(Ans. 0.157 M)

(e) Calculate the number of moles of citric acid in 250 mL of a 0.400 M solution of citric

acid. (Ans. 0.100 mole)

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(f) Calculate the volume (in mL) of a 0.355 M NaOH solution which would contain 0.200

mole of NaOH. (Ans. 563 mL)

(g) Calculate the mass of Na2CO3 that must be used to make 700 mL of a 0.136 M Na2CO3

solution.

Solution: MM of Na2CO3 = (23.0x2)+12.0+(16.0x3) = 106

M = n = MV = 0.136 mol/L x 0.700 L = 0.0952 mol

n

V

mass of Na2CO3 = 0.0952 mol x 106 g/mol = 10.1 g

(h) What mass of NaOH is needed to make 200 mL of a 0.300 M NaOH solution? (Ans. 2.40 g)

(i) What volume (in mL) of 0.200 M NaOH can be made from 1.20 g of NaOH?

Solution: moles NaOH = = 0.0300 mole

1.20 g

40.0 g/mol

M = V = = = 0.150 L = 150 mL