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which laboratory activities involve chemical changes? check all that apply.

leaving a copper penny in vinegar until it turns green
boiling saltwater for several minutes until only solid salt remains
extracting iron filings from a sand mixture using a magnet
crushing a rock with a hammer to extract mineral deposits
putting an iron nail outside for a month and observing changes

The correct activities are leaving a copper penny in vinegar until it turns green, and putting an iron nail outside for a month and observing changes.

Explanation:

The formation of the green component on the copper penny and the formation of rust on the iron nail when kept outside for a month are the illustrations of chemical changes. On the other hand, extracting fillings or iron from a sand mixture with a magnet, boiling salt water away, and crushing rock with a hammer are the illustrations of physical modifications.

you didnt put any of the following

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol