Some compounds exist in a “hydrated” state. Hydrated Compounds Some compounds exist in a “hydrated” state. Some specific number of water molecules are present for each molecule of the compound.

Dessicants You’ve probably noticed that some consumer goods contain a small packet labeled “Silica gel: Do not eat”. What’s that packet for, anyway?

As you know, many fragile goods can be easily damaged by moisture As you know, many fragile goods can be easily damaged by moisture. The silica gel in each packet is used to soak up water from the atmosphere. This minimizes moisture that causes damage during shipping.

Many ionic compounds can be used to soak up water Many ionic compounds can be used to soak up water. Before they absorb water, they’re referred to as “anhydrous”, which means “without water”.

What is a Hydrate? Any salt that has water chemically bonded to the ions in the crystal structure is a hydrate or hydrated crystal. Copper(II) sulfate is a hydrate. Hydrated copper(II) sulfate is deep blue in color.

After they’ve soaked up the maximum amount of water, they’re called “hydrates”, making that water molecules are stuck to them

If you heat hydrates to very high temperatures, they “dehydrate”, meaning that the water is lost. Once all of the water is lost, these compounds are again referred to as “anhydrous”.

What does the Chemical Formula of A Hydrate Look Like? BaCl2•2H2O FeSO4•6H2O Na2CO3•10H2O

How are Names of Hydrates Written? BaCl2•2H2O barium chloride dihydrate FeSO4•6H2O iron(II) sulfate hexahydrate Na2CO3•10H2O sodium carbonate decahydrate

What prefixes are used? 0.5 hemi 7 hepta 1 mono 8 octa 2 di 9 nona 3 tri 10 deca 4 tetra 11 undeca 5 penta 12 dodeca 6 hexa 13 triskaideca

Example: A 7.62 g sample of hydrated calcium nitrate is heated to constant mass. Find the percent water in the hydrate and the formula for it if 5.28 grams remains after heating How much water was driven off from the hydrate? What is the empirical formula of calcium nitrate hydrate?

Example: 1. Determine Mass of H2O driven off 7.62 g Ca(NO3)2 hydrate – 5.28 g Ca(NO3)2 anhydrous = 2.34 g water 2. Determine Moles of water and anhydrous salt 2.34 g H2O x (1mol H2O/ 18.02 g H2O) = 0.130 mol H2O 5.28 g Ca(NO3)2 x (1mol Ca(NO3)2 / 164.1g Ca(NO3)2 )= 0.0321 molCa(NO3)2 3. Find the whole number ratio 0.130 mol H2O/ 0.0321 molCa(NO3)2 = 4.04 ≈ 4 0.03 molCa(NO3)2 /0.0321 molCa(NO3)2 = 1 Answer: Ca(NO3)2 • 4H2O

Example #2: Anhydrous lithium perchlorate (4.78 g) was dissolved in water and re-crystalized. Care was taken to isolate all the lithium perchlorate as its hydrate. The mass of the hydrate salt obtained was 7.21g. What is the formula for the hydrate? Answer: LiClO4 • 3H2O