STOIchio METRY Lesson 2 Molar Concentration Remember that

STOIchio. METRY! Lesson 2

Molar Concentration • Remember that concentration is c = n/v • Stoichiometry is the relationship between the moles. • We can rearrange the equation to solve for moles by • n = cv • NOTE – If volume is mentioned, we cannot ASSUME the volume is 22. 4 L. We can only use 22. 4 L if the given information is a GAS and at STP!

Example • What mass of barium phosphate will result if 139. 0 m. L of 5. 000 M barium bromide reacts with sodium phosphate? • 3 Ba. Br 2 + 2 Na 3 PO 4 → Ba 3(PO 4)2 + 6 Na. Br • NOTE – We must always convert to moles to cross the mole bridge!

Example • What volume of CO 2(g) at STP is produced if 1. 35 L of 0. 100 M HCl reacts with excess Ca. CO 3?

Titration • It is a special process we use to find an unknown concentration of a chemical • We can do this if we know the EXACT VOLUME and CONCENTRATION of one species and the VOLUME of our unknown species • We use a tool called a burette (will use a lot in chemistry 12)

Equivalence point or stoichiometric point • This is the point when the molar ratio between our known species and unknown species meet the molar ratio of the balanced reaction! • Their mole ratio matches the coefficients! • We use an indicator that changes colour when the equivalence point is met! (more on this in chemistry 12) • One indicator is phenolphthalein, the indicator that turns pink!

Example • H 2 SO 4 + 2 Na. OH → Na 2 SO 4 + 2 H 2 O • For this example, our equivalence point is met when 1 mole of H 2 SO 4 is reacted with 2 moles of Na. OH. Any ratio of 1: 2 will work • This means if we have a known concentration of 0. 05 mol of H 2 SO 4. We will need 0. 10 mol of Na. OH to meet its equivalence point!

Example • It takes 19. 54 m. L of 0. 50 M Ba. Br 2 to titrate 25. 0 m. L of Na 3 PO 4. Find [Na 3 PO 4]

Remember • In a titration, the equivalence point is when the mole ratios are met! • 3 A + 2 B → 3 C • The equivalence point is met when we have any ratio of 3 A to 2 B.

Homework • Page 131 #17 -25 (odd only)