Formula of a Hydrate What is a hydrate

Formula of a Hydrate

What is a hydrate? • An ionic compound that contains water molecules in its structure • The formula states how many mol of water molecules per one mol of ionic compound • Example: Cu. So 4 5 H 20 Copper sulfate pentahydrate

What is an anhydrate? • The substance that remains after the water is removed from a hydrate • Example: Cu. So 4 Anhydrous Copper sulfate

Prefixes 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca

Steps to find formula 1. Identify what’s given: A. Hydrate/anhydrate (go to step 2) B. Anhydrate/water (skip to step 3) 2. If given hydrate and anhydrate, subtract to get water 3. Convert mass of anhydrate and water to moles of each, respectively 4. Find the ratio of water to anhydrate (in moles) 5. Write the formula; ionic compound followed by ratio of water 6. Name the compound

Example 1 A calcium chloride hydrate has a mass of 4. 72 g. After heater for several minutes the mass of the anhydrate is found to be 3. 56 g. Determine the formula and name of the hydrate. 2+ Calcium chloride: Ca Step 2: 4. 72 g hydrate Cl− − 3. 56 g anhydrate 1. 16 g H 2 O Ca. Cl 2 Step 3: 3. 56 g Ca. Cl 2 1 mol Ca. Cl 2 = 0. 0321 mol. Ca. Cl 2 110. 98 g Ca. Cl 2 1. 16 g H 2 O 1 mol H 2 O = 0. 0644 mol H 2 O 18. 02 g H 2 O SIG FIGS IN ANSWER MUST MATCH GIVEN!!

Step 4: Ratio 0. 0644 mol H 2 O 0. 0321 mol Ca. Cl 2 ≈ 2 1 Step 5: Ca. Cl 2 2 H 2 O Step 6: calcium chloride dihydrate

Example 2 What is the formula an name for a hydrate which consists of 76. 9% Ca. SO 3 and 23. 1% H 2 O? Step 3: 76. 9 g Ca. SO 3 1 mol Ca. SO 3 = 0. 640 mol Ca. SO 3 110. 98 g Ca. SO 3 23. 1 g H 2 O 1 mol H 2 O 18. 02 g H 2 O = 1. 28 mol H 2 O SIG FIGS IN ANSWER MUST MATCH GIVEN!!

Step 4: Ratio 1. 28 mol H 2 O 0. 640 mol Ca. SO 3 Step 5: Ca. SO 3 2 H 2 O Step 6: calcium sulfite dihydrate ≈ 2 1