Chemistry Questions

1. A student prepared a 0.12 M aqueous solution by dissolving 4g of solid NaOH in distilled water. What volume (in cm³) of the NaOH(aq) can he get ?
(relative atomic masses:H=1.0, O=16.0, Na=23.0)

Molar mass of NaOH = 23 + 16 + 1 = 40 g/mol
No. of moles of NaOH = 4/40 = 0.1 mol
Volume of NaOH(aq) = mol/M = 0.1/0.12 = 0.833 dm³ = 833 cm³


2. What are the molarities of the constituent ions if 25.0 g of sodium carbonate-10-water crystals(Na2CO3•10H2O) are dissolved in distilled water and made up to 250.0 cm³?
(relative atomic masses:H=1.0, C=12.0, O=16.0, Na=23.0)

Molar mass of Na2CO3•10H­2O = 23x2 + 12 + 16x3 + 10(1x2 + 16) = 286 g/mol
No. of moles of Na2CO3•10H­2O = 25/286 = 0.0874 mol
Volume of the solution = 250 cm³ = 0.25 dm³
Molarity of the solution = 0.0874/0.25 = 0.35 M
Molarity of Na^+ ions = 0.35 x 2 = 0.7 M
Molarity of CO3^2- ions = 0.35 M

1.A student prepared a 0.12M aqueous solution by dissolving 4g of solid
NaOH in distilled water. What volume(in cm^3) of the NaOH(aq) can he
get?
(relative atomic masses:H=1.0, O=16.0, Na=23.0)

molecular mass of NaOH= 23+16+1=40g/mol
4g NaOH = 1/10 mol NaOH
let the volume of NaOH(aq)=xdm^3
then (1/10)mol/xdm^3=0.12M
x=5/6
so the volume =5/6 dm^3=833 cm^3( corr to 3 sig. fig.)


2.What
are the molarities of the constituent ions if 25.0g of sodium
carbonate-10-water crystals(Na2CO3 ‧ 10H2O) are dissolved in distilled
water and made up to 250.0 cm^3?
(relative atomic masses:H=1.0, C=12.0, O=16.0, Na=23.0)

molecular mass of Na2CO3 = 23*2+12+16*3=106 g/mol
so 25 g Na2CO3 = 0.236 mol Na2CO3
then the molarities =
0.236 mol/0.25 dm^3=0.943 M (corr to 3 sig. fig.)