Law of Law of Conservation of Conservation of Mass (LCM)Mass (LCM)

Law of conservation of mass Law of conservation of mass – states that mass is neither – states that mass is neither created nor destroyed during created nor destroyed during chemical reactions or physical chemical reactions or physical changeschanges

Reactant – substance that Reactant – substance that undergoes a reactionundergoes a reaction

Product – a new substance Product – a new substance formed when reactants formed when reactants undergo chemical changeundergo chemical change

Balanced equation - An Balanced equation - An equation for a chemical reaction equation for a chemical reaction in which the number of atoms in which the number of atoms for each element in the reaction for each element in the reaction and the total charge are the and the total charge are the same for both the reactants and same for both the reactants and the products. In other words, the the products. In other words, the mass and the charge are mass and the charge are balanced on both sides of the balanced on both sides of the reaction.reaction.

Coefficients – a number Coefficients – a number placed in front of the parts of placed in front of the parts of a chemical equation to a chemical equation to indicate how many are indicate how many are involved ; always a positive involved ; always a positive whole number.whole number.

Subscript – Subscript –

Formula – a combination of Formula – a combination of chemical (element) symbols that chemical (element) symbols that show what elements make up a show what elements make up a compound and the number of compound and the number of atoms of each elementatoms of each element

Chemical equation - A symbolic Chemical equation - A symbolic representation of what happens representation of what happens when chemicals come in contact when chemicals come in contact with one another.  A balanced with one another.  A balanced chemical equation shows how chemical equation shows how many of what molecules react, many of what molecules react, how many of what molecules how many of what molecules result, and sometimes the state result, and sometimes the state of the substances.of the substances.

Demo:LCM – in chemical reactions, you always end up with the same amount of stuff you start with.“Stuff” – very scientific could be atoms or mass.

Demo:What is the formula for aluminum chloride?

What is the formula for copper chloride?

Demo:What will happen if I drop aluminum into a copper chloride solution?

Demo:Write the chemical reaction…

CuCl2 + Al → AlCl3 + Cu

Do you notice anything?!

Demo:Balance the chemical reaction…

3CuCl2 + Al → AlCl3 + Cu3CuCl2 + Al → 2AlCl3 + Cu3CuCl2 + Al → 2AlCl3 + 3Cu3CuCl2 + 2Al → 2AlCl3 + 3Cu

__Ca(C__Ca(C22HH33OO22))22 + __K + __K33POPO44 __Ca__Ca33(PO(PO44))22 + + __KC__KC22HH33OO22

  Which set of coefficients Which set of coefficients balances the equation? balances the equation?   A. 3, 3, 1, 2A. 3, 3, 1, 2B. 6, 1, 1, 3B. 6, 1, 1, 3C. 3, 2, 1, 6C. 3, 2, 1, 6D. 6, 2, 1, 6D. 6, 2, 1, 6

Each answer is on the

following slide.

Which of these would support the Which of these would support the idea that mass is conserved in a idea that mass is conserved in a reaction that produces a gas as a reaction that produces a gas as a product? product?   A. Heating the reactants to ensure A. Heating the reactants to ensure the reaction occurs in a gaseous the reaction occurs in a gaseous statestateB. Subtracting the mass of the gas B. Subtracting the mass of the gas from the mass of the solid and liquid from the mass of the solid and liquid productsproductsC. Mixing the reactants and C. Mixing the reactants and measuring their total mass measuring their total mass D. Trapping the gas and measuring D. Trapping the gas and measuring its massits mass

C

Aluminum metal and oxygen Aluminum metal and oxygen gas combine to produce gas combine to produce aluminum oxide (Alaluminum oxide (Al22OO33). ). Which of these is the Which of these is the balanced equation for this balanced equation for this reaction? reaction?   A. Al + OA. Al + O22 Al Al22OO33

B. 2Al + 2OB. 2Al + 2O22 2Al 2Al22OO33

C. 2Al + 3OC. 2Al + 3O22 5Al 5Al22OO33

D. 4Al + 3OD. 4Al + 3O22 2Al 2Al22OO33

D

CaCOCaCO3 3 CaOCaO + CO+ CO2 2

The chemical equation shows CaCOThe chemical equation shows CaCO33 being heated. Which of these being heated. Which of these statements best describes the mass statements best describes the mass of the products if 100 g of CaCOof the products if 100 g of CaCO33 is is heated? heated?   

A. A. The difference in the products’ The difference in the products’ masses is equal to the mass of the masses is equal to the mass of the CaCOCaCO33. . B. The sum of the products’ masses is B. The sum of the products’ masses is less than the mass of the CaCOless than the mass of the CaCO33. . C. The mass of each product is equal to C. The mass of each product is equal to the mass of the CaCOthe mass of the CaCO33..D. The sum of the products’ masses D. The sum of the products’ masses equals the mass of the CaCOequals the mass of the CaCO33. .

D

Which chemical equation Which chemical equation supports the law of supports the law of conservation of mass? conservation of mass?   A. 2HA. 2H22O(O(ll) ) H H22((gg) + O) + O22((gg) ) B. Zn(B. Zn(ss) + HCl() + HCl(aqaq) ) ZnCl ZnCl22((aqaq) + ) + HH22((gg) ) C. AlC. Al44CC33((ss) + H) + H22O(O(ll) ) CH CH44((gg) + ) + Al(OH)Al(OH)33((ss) ) D. CHD. CH44((gg) + 2O) + 2O22((gg) ) COCO22((gg) + ) + 2H2H22O(O(gg) )

D

2Cu + O2Cu + O22 2CuO 2CuO When 127 g of copper reacts When 127 g of copper reacts with 32 g of oxygen gas to form with 32 g of oxygen gas to form copper (II) oxide, no copper or copper (II) oxide, no copper or oxygen is left over. How much oxygen is left over. How much copper (II) oxide is produced? copper (II) oxide is produced?

A. 32 gA. 32 gB. 95 gB. 95 gC. 127 gC. 127 gD. 159 gD. 159 g

D

K + HK + H22O O KOH + H KOH + H22

What is the coefficient for HWhat is the coefficient for H22O O when the above equation is when the above equation is balanced? balanced?   A. 1 A. 1 B. 2B. 2C. 3C. 3D. 4D. 4

D

According to the law of According to the law of conservation of mass, how much conservation of mass, how much zinc was present in the zinc zinc was present in the zinc carbonate? carbonate? A. 40 gA. 40 gB. 88 gB. 88 gC. 104 gC. 104 gD. 256 gD. 256 g

B

What are the coefficients that What are the coefficients that will balance this chemical will balance this chemical equation? equation? A. 2, 1, 1A. 2, 1, 1B. 3, 4, 2B. 3, 4, 2C. 2, 2, 1C. 2, 2, 1D. 4, 3, 2D. 4, 3, 2

C

The illustrations show a The illustrations show a conservation-of-mass conservation-of-mass experiment. The experiment. The solution in the beaker solution in the beaker lost mass because lost mass because _____. _____.

A. materials have less A. materials have less mass at mass at high temperatures high temperatures

B. the mass of the B. the mass of the reactants reactants and products was and products was less less than 100 g than 100 g

C. sodium sulfate C. sodium sulfate (Na(Na22SOSO44) is ) is lighter than air lighter than air

D. some of the water D. some of the water molecules turned molecules turned into gasinto gas

C

D