1. Observations: Appearance of penny in vinegar after 30 minutes
2. Classify the reaction between zinc and acetic acid.
3. What evidence was there that a reaction was taking place?
1. Observations: Appearance after initial mixing. Appearance after 30 minutes
2. Classify the reaction between magnesium sulfate and ammonia.
3. What evidence was there to indicate that the Epsom salts and ammonia reacted?
You didn't include your observations, but I can address what usually occurs in these two chemical reactions.
Penny in vinegar:
Since you mentioned Zinc, you must have scraped away some of the copper outer surface of the penny to expose the zinc core of the penny.
1. Penny after 30 minutes - copper isn't very reactive with vinegar, which is 5% acetic acid. It's unlikely that there would be enough of a reaction to observe a change in the copper itself after 30 minutes. You may have noticed that the color of the penny changed such that it looked newer after being in vinegar. Acetic acid reacts with the copper oxide, removing the coating produced by the oxidation of the penny over time.
2. When vinegar reacts with the exposed zinc hydrogen is generated via the following reaction, which is classified as single replacement:
`Zn_(s) + 2 CH_3COOH_(aq) -> Zn(CH_3COO)_(aq) + H_2_(g)`
3. The evidence of a chemical reaction that you're most likely to see immediately is the formation of hydrogen gas bubbles at the surface of the zinc.
Magnesium Sulfate and ammonia:
1. When aqueous ammonia is added to magnesium sulfate a cloudy white precipitate usually forms.
This is an example of a double replacement or precipitation reaction:
`2 NH_4OH_(aq) + MgSO_4(aq) -> Mg(OH)_2_(s) + (NH_4)_2SO_4_(aq)`
Ammonia hydrolyzes water to produce NH4+ and OH- in solution. The product Mg(OH)2 is insoluble, that's why you see cloudiness when the two substances mix.
The net ionic equation, leaving out spectator ions, is:
`Mg^(2+) + 2 OH^(-) -> Mg(OH)_2_(s)`
3. The cloudiness observed is evidence that a chemical reaction occurred.