Experiment Chemical and physical changes

EXPERIMENT: CHEMICAL AND PHYSICAL CHANGES

Lab partner

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Abstract

Matter undergoesthrough two types of changes physical and chemical changes. Physicalchanges are brought about by physical forces which results in changein form or the physical properties of a given substance withoutformation of a new substance or need of chemical reaction. Chemicalchanges are caused by chemical reaction which causes new substancesto be formed. In this experiment, the physical and chemical changethat occurs when certain substances are subjected to physical forcessuch as heat, and chemical reactions were studied (Alpert, A. 2008).

Purpose

The experimentwas performed to study the physical and chemical changes that matterundergoes when it is subjected to physical forces and chemicalreaction. The experiment will help in developing understanding of thetheory behind chemical and physical changes.

Experiment andobservation

The procedurethat was used in this experiment was adapted from Lab Manual,Observation of physical and chemical changes.

Table 1

Well.

Chemical 1

(4 drops)

Chemical 2

(4 drops)

Observations

Chemical change

(Y/N)

A1

NaHCO3

HCl

Effervescence with no color change. Clear solution was formed

Y

A2

NaOCl

KI

Clear solution with no color change with grey solid at the bottom.

No color change when 2 drops of starch were added.

Y

A3

KI

Pb(NO3)2

Yellow solid precipitated from the solution

Y

A4

NaOH

C20H14O4

Light purple solution was formed.

Y

A5

HCl

C20H14O4

No color change

N

A6

AgNO3

NH4OH

Cloudy white solution was formed

Y

B1

NaOH

AgNO3

Color changed to green

Color changed to brown precipitate on exposure to sunlight

Y

Y

B2

NH4OH

CuSO4

Light blue cloud was formed

Y

Table 2

Chemical

Observation

Initial

Heating

Burning

Mg

Silver color turnings

Copper color

White powder

Zn

Silver color, large

Yellow color

Turnishes

CuCO3

Green powder

Change to brown

Brown powder

Cu(NO3)2

Blue power

Blue powder turns green

Color changes to blue

Discussion

Since thisexperiment is qualitative, there was no requirement for calculations.Errors could emerge from contamination of apparatus that was used tocarry out the chemical reactions. Contamination could also alter thephysical changes when the various substances were subjected toheating and burning.

During theexperiment, observations made on the chemicals used when subjected toheating, burning and chemical reactions were used to determinewhether they undergone chemical/physical changes or not. Theobservations were based on the difference between the final substancefrom the initial substance for a chemical change, and the differencebetween the initial appearances from the final appearance. A goodexample of the chemical change is the reaction of sodium bicarbonateand hydrochloric acid that is represented by the equation below

NaHCO3(aq)+ HCl(aq)→CO2(g) + H2O(l) + NaCl(aq)

New substances, CO2(g) + H2O(l) + NaCl(aq),were formed. The effervescence that was observed was due to thecarbon (IV) oxide gas formed. Physical changes in this experimentwere noted due to color change and physical state. Odor can also beused to tell physical changes.

Questions

(the questions between A to J were obtained from “observation ofChemical and Physical Changes” LabPaq Lab Manual.)

Q.A

Based on the table on chemical reaction, sodium bicarbonate producescarbon (IV) oxide gas as one of its products when reacted with anacid. A sample of the household product is taken and then reactedwith HCl. When gas bubbles are observed during the reaction betweenthe product and hydrochloric acid, carbon (IV) oxide gas is produced.This will show if the product contains sodium bicarbonate.

Q.B

Well A6 reaction

AgNO3(aq) +NaOH(aq)→AgOH(s) + NaNO3(aq)

Q.C

Well A1 wasresponsible for the production of CO2(g) + H2O(l)+ NaCl(aq). The observation made where gas is produced wascharacterized with bubbles (effervescence), and it is only well A1which had gas bubbles produced when sodium carbonate was reacted withan acid.

Q. D

Phenolphthaleinis colorless in acidic solutions, and since vinegar is an acid, itshould follow suit. The sample does not contain vinegar because inturned to pink instead of colorless which an acid should.

Q. F

Testing for thepresence of lead in the hair tonic, it is reacted with nitric acid inorder to form lead nitrate. The product formed is reacted with KI.When yellow solid is precipitated, the results will be positive butit is negative when yellow solid is not formed.

Q. H

The change is notchemical change since no chemical reaction was involved. The changewas due to a change of pressure and is experienced when the bottle isopen. Pressure is a physical force that is results into the carbon(IV) oxide gas bubbles produced from dissolved carbon (IV) oxide. Nonew product is formed and, therefore, the change cannot be said to bechemical (Gregg, D. C. 1958).

Q. I

In well B1, thesecond reactant used was hydrochloric acid. The chemical change isresulted as silver chloride is formed.

Q. J

Phenolphthaleinis an indicator, and it is colorless in acidic solutions like in wellA5 which had hydrochloric acid. It should produce clear and colorlesssolution in acids (Hill, G. C., &amp Holman, J. S. 2000).

AdditionalQuestion Guidelines:

Q1

&nbsp

Unknown

Phenolphthalein

The phenolphthalein turned the unknown pale pink.

NaHCO3

No reaction was seen

Pb(NO3)2

White solid (precipitate formed)

AgNO3

Nothing happened

The unknown is abase since it turns phenolphthalein pink. The base probably is sodiumhydroxide since it cannot react with sodium bicarbonate and silvernitrate, but it reacts with lead nitrate to form insoluble leadhydroxide that is the white solid (precipitate) formed.

Q2.

CuCO3(s)→CuO(s)+ CO2(g)

Q3

2Mg(s) + O2 (g)→2MgO(s)

References

Alpert, A. (2008).&nbspMilady`s standard cosmetology. CliftonPark, NY: Cengage Learning.

Gregg, D. C. (1958).&nbspPrinciples of chemistry. Boston:Allyn and Bacon.

Hill, G. C., &amp Holman, J. S. (2000).&nbspChemistry incontext. Walton-on-Thames: Nelson.

Kotz, J. C., Treichel, P., &amp Townsend, J. R. (2009).&nbspChemistry&amp chemical reactivity. Belmont, Calif: Thomson Brooks/ Cole.