5 Simple Steps to Solve Solution Stoichiometry Problems
1. Figure out if it’s an M = n/V problem or a McVc = MdVd problem
Published in
2 min readFeb 12, 2017
- M = n/V
- What the formula means:
- Molarity = number of moles / Volume (L)
- Key words:
- “react/reaction”
- “titrate/titration”
- What they’ll give you:
- They’ll give you the concentration/molarity, volume, or mass of one substance in a chemical reaction and you have to convert it to another substance
- two of the three variables between M, n, and V
- McVc = MdVd
- What the formula means:
- Molarity of Diluted solution x Volume of Diluted solution = Molarity of Concentrated solution x Volume of Concentrated solution
- this is a rearranged version of n=MV, basically saying moles of concentrated solute = moles of diluted solute
- Key words:
- “dilute”
- “add water” or “mix with water”
- “concentrated solution” or “stock solution”
- What they’ll give you:
- multiple molarities/concentrations for the same substance
- multiple volumes for the same substance
- a volume of water being added
2. See what you need to solve for
- “how many moles” / “what mass”
- solve for n → n = MV → convert moles to grams if necessary
- “what volume” / “how much solution”
- solve for V → V = n / M
- “what concentration” / “what molarity”
- solve for M → M = n / V
- “how would you prepare X solution”
- find out the number of moles of solute, then convert that to grams and say
3. For M=n/V, convert everything to moles
- Moles are the currency that allows you to convert from one substance to another
- Once you’ve converted to moles, you can use a mole bridge to switch between substances in a reaction based on their coefficients
4. For McVc=MdVd, solve for 3 of the 4 variables
- Sometimes, you will have to calculate the volume of the diluted solution
- Vd = Vc + Vwater
5. For “How would you prepare X solution” problems…
- If it’s an n=MV problem:
- Find the mass of solute after finding moles of solute and the volume of the desired solution
- Say “add enough water to X grams of [solute] to make Y liters of [desired solution]”
- If it’s a problem where you want to dilute a concentrated solution:
- Find the volume of concentrated solution and the volume of water added to make the diluted solution
- Say “add X liters of water to Y liters of [concentrated molarity]M solution”