Question

A 4 g sample of sodium hydroxide, NaOH, is dissolved in water and made up to 500 cm3 of aqueous solution. What is the concentration of the resulting solution?

Answer 1

Concentration in molarity is 2 M.

Step-by-step explanation:

Mass of NaOH dissolved = 4 g

Molar mass of NaOH = 40 g/mol

Number of moles =
`(Given\ mass)/(molar\ mass)=(4)/(40)=0.1\ mol`

Concentration is usually expressed in terms of molarity.

Molarity is defined as number of moles of solute per litre of solution.

Molarity =
`(Number\ of\ moles\ of\ solute)/(Volume\ of\ solution\ in\ L)`

=
`(0.1*1000)/(500)=0.2\ M`

Hence concentration of the solution is 2 M.

Answer 2

0.2 M is the concentration of the resulting solution

Step-by-step explanation:

M is a unit for concentration which means mole of solute in 1L of solution.

According to the received information, we have 4 g in 500 mL of solution.

In 0.5L we have 4 g of solute

In 1L we have (1 .4)/0.5 = 8 g of solute

Let's convert the mass in mole

Mass / Molar mass = Mole

Molar mass NaOH = 40 g/m

8g / 40 g/m = 0.2M