Solve a problem

Solutions and concentrationChemistryHigh schoolabout 0:57

10 g of NaOH is dissolved in water to make 250 mL of solution. What is the molarity?: animated lesson

A narrated, step-by-step solutions and concentration video lesson with captions. Final answer: M = 1.00008 mol/L.

SpeedLanguage

Video with a synthetic English voice and captions. Pick another language for subtitles in that language, or open the interactive version.

Video narrated by a synthetic voice (Piper TTS, en_US-ljspeech-high voice (LJ Speech dataset, public domain)); the steps come from our maths engine and the answer was checked independently. Download MP4 (0.4 MB) · Captions (WebVTT)

Steps on screen

1. The problem
Worked example
10 g of NaOH is dissolved in water to make 250 mL of solution. What is the molarity?
2. Step by step
1. $M(\mathrm{NaOH}) = 39.997\ \text{g/mol}$
  Molar mass of NaOH
2. $n = \frac{m}{M} = \frac{10\ \text{g}}{39.997\ \text{g/mol}} = 0.250019\ \text{mol}$
  Convert grams to moles
3. $V = \frac{250\ \text{mL}}{1000} = 0.25\ \text{L}$
  Convert the volume to litres
4. $M = \frac{n}{V} = \frac{0.250019\ \text{mol}}{0.25\ \text{L}} = 1.00008\ \text{mol/L}$
  Molarity is moles per litre
3. The answer
$\text{M = 1.00008 mol/L}$
M = 1.00008 mol/L
4. Check
- n = MV: 1.00008 × 0.25 = 0.250019 mol ✓

Transcript

The problem. Here is the problem: 10 g of NaOH is dissolved in water to make 250 mL of solution. What is the molarity? Molarity is moles of solute per litre of solution.

Step by step. Molar mass of NaOH. Convert grams to moles. Convert the volume to litres. Molarity is moles per litre.

The answer. So the answer is M equals 1.00008 mol/L. Molarity (mol/L, written M) uses the volume of the whole solution, not of the solvent alone. To make a solution, weigh the solute, dissolve it in less solvent, then top up to the final volume.

Check. n equals MV: 1.00008 times 0.25 equals 0.250019 mol, which checks out.

About solutions and concentration

Molarity, dilution and moles of solute in a solution.

10 g of NaOH is dissolved in water to make 250 mL of…