Classifying Chemical Reactions Lab Answers

Classifying Chemical Reactions LABObservations listed below for 7 reactions and QUESTIONS

OBSERVATIONSReaction 1:The zinc metal is dull to start with&disappears as the reaction proceeds.Bubbles form around zinc.Reaction 2:hydrogen peroxide is colourless and MnO2(s)is black.The solution bubbles alot when MnO2(s)is added.The gas that is produced looks smoky causes the glowing splint to burst into flames.The solution remain colourless.

Reaction 3:copper wire is shiny to start with & glows red hot when in the burner flame.wire becomes dull after 2 min of heating.

Reaction 4:Both solutions are colourless to start with,but when mixed,they become milky in colour.

Reaction 5:The CuSO4*5H2O(s)is blue to start with & gradually turns white with heating.Drops of liquid form on neck of the test tube.

Reaction 6:white solid turns blue when few drops of H2O are added.test tube gets warmer after water is added.

Reaction 7:The iron nail is shiny to start with&the solution is blue.The nail gets a dark coating&the solution turns lighter blue with time.Closer look of nail shows a coppery colored substance on it.

QUESTIONS1Write balanced equation for all 7 reactions including state of particpants(s,l,g) and classify reaction as synthesis,decomposition,SR,DR2The copper wire in reaction 3 essentially burned in air.What part of the air did the copper react with?3Cu+2(aq) ions are the cause of the blue colour in the copper(II) sulphate solution.In reaction7,what is indicated by the colour change in the solution?4)2common observations where chemical change occured?

Expert Answers

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Balanced Equations:

you did not state what was added to the Zn so lets assume HCl.

Zn (s) +2 HCl (aq) -->  ZnCl2 (aq) + H2 (g)  Single replacement

In the second reaction the MnO2 acts as a catalyst in the decomposition of hydrogen peroxide.

2 H2O2 (aq) --> 2 H2O (aq) + O2 (g)


Reaction 3 is a synthesis reaction:

2 Cu (s) + O2 (g) --> 2 CuO (s)


Reaction 4 is a double replacement reaction.  The general form is:

AB (aq) + CD (aq) --> AC (aq)  + BD (s)


reaction 5 is a decomposition or dehydration type reaction:

CuSO4*5HOH (s) --> CuSO4 (s) + 5 HOH (l)


Reaction 6 is a synthesis or hydration reaction:

CuSO4 (s) + 5 HOH (l) -->  CuSO4*5HOH (s)

Reaction 7 is a single replacement reaction and is also an oxidation-reduction reaction>  The iron is oxidized and the copper is reduced.

Fe (s) + CuSO4 (aq)--> FeSO4 (aq)+ Cu (s)

Question 2:  the copper is combining with the oxygen in the air.


Question 3: the copper ion is being reduced to the element so the blue color gradually disappears.

Question 4:  common signs of a chemical reaction are:  release of heat or a gas; formation of a precipitate; change in color.

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