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Solutions and concentrationChemistryHigh schoolabout 0:59

11.1 g of CaCl2 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 = 0.400079 mol/L.

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. 1. The problem
    Worked example
    11.1 g of CaCl2 is dissolved in water to make 250 mL of solution. What is the molarity?
  2. 2. Step by step
    1. M(CaCl2)=110.978 g/molM(\mathrm{CaCl_{2}}) = 110.978\ \text{g/mol}
      Molar mass of CaCl2
    2. n=mM=11.1 g110.978 g/mol=0.10002 moln = \frac{m}{M} = \frac{11.1\ \text{g}}{110.978\ \text{g/mol}} = 0.10002\ \text{mol}
      Convert grams to moles
    3. V=250 mL1000=0.25 LV = \frac{250\ \text{mL}}{1000} = 0.25\ \text{L}
      Convert the volume to litres
    4. M=nV=0.10002 mol0.25 L=0.400079 mol/LM = \frac{n}{V} = \frac{0.10002\ \text{mol}}{0.25\ \text{L}} = 0.400079\ \text{mol/L}
      Molarity is moles per litre
  3. 3. The answer
    M = 0.400079 mol/L\text{M = 0.400079 mol/L}

    M = 0.400079 mol/L

  4. 4. Check
    • n = MV: 0.400079 × 0.25 = 0.10002 mol ✓

Transcript

The problem. Here is the problem: 11.1 g of CaCl2 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 CaCl2. Convert grams to moles. Convert the volume to litres. Molarity is moles per litre.

The answer. So the answer is M equals 0.400079 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: 0.400079 times 0.25 equals 0.10002 mol, which checks out.

About solutions and concentration

Molarity, dilution and moles of solute in a solution.

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