# Tutor profile: Toni H.

## Questions

### Subject: Inorganic Chemistry

What is the electron configuration of Co?

Looking at a periodic table we see the last noble gas to appear before Cobalt is Argon. From there, we go thru the 4s row, and 7 elements into the 3d row. This give an electrion configuration of [Ar] 4s2 3d7

### Subject: Chemistry

You are given 3.50 g of Ca(NO3)2 and 5.00 g of Na2SO4. What is the precipitate you will yield, and how many grams of it will you obtain?

Start by writing the balanced double displacement equation. Ca(NO3)2 + Na2SO4 --> CaSO4 + 2 NaNO3 Per solubility rules, we know that all nitrates (NO3-) soluble. So NaNO3 is not our precipitate. Sulfates (SO4(2-)) are soluble, except when formed with Ca2+. This makes CaSO4 our precipitate. In order to find out how much of the precipitate is formed, we need to find the limiting reagent. If we have 3.50 g of Ca(NO3)2, and the molar mass of that reagent is 164.1 g/mol, we divide our weight by the molar mass, and we have 0.0213 mol Ca(NO3)2. We have 5.00 grams of Na2SO4, which has a molar mass of 142.1 g/mol, leading us to have 0.0352 g. Since we have less moles of the Ca(NO3)2, that is our limiting reagent. Using stoichiometry and a balanced equation, we conclude that we then have 0.0213 moles of the precipitate, CaSO4, since they are at a 1:1 ratio. This precipitate has a molar mass of 137.2 g/mol so if we take that and multiply it by our moles, we get 2.92 grams of CaSO4.

### Subject: Basic Chemistry

Which of the following is an alkali metal? A- Cadmium B- Rubidium C- Barium D- Titanium

Alkali metals are the first group (column) of the periodic table. Looking at the periodic table, Rubidium is the only element of the choices in this column, making it the alkali metal.

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