What is a replacement reaction?

Transcription

1 I Lesson What is a replacement? KEY TERM replacement : in which one kind of matter replaces another kind 97

2 LESSON 16 What is a replacement? Imagine that three children are playing. Two are holding hands. The other is alone. The child that was alone now joins the others. He takes the place of one of the children. Now a different child is alone. We have the same children that we started with. But now they are arranged in a different way. Some chemical s work like this. A free element takes the place of or replaces another element of a compound. The element that was replaced is now "free.", A + BC AC + B free element compound new compound new free element Let's study an actual replacement -one hydrochloric acid (HCI). between zinc (Zn) and The zinc is the" free" element. The hydrochloric acid is in the compound. Zn 2HCl ZnCl2 + H2 + The zinc replaces the hydrogen. The hydrogen is set free. The produces a new compound, zinc chloride (ZnCI 2 ),and free hydrogen (H 2 ).Notice that the elements we started with are the elements we ended with. They are just arranged in a different way. This kind of is called a single replacement. In a single replacement, a free element replaces a different element of a compound. 98

3 UNDERSTANDING SINGLE REPLACEMENT REACTIONS copper sulfate solution iron nail What You Need (Materials) iron nail copper sulfate solution beaker How To Do The Experiment (Procedure) Place an iron nail in copper sulfate solution. Figure A Remove the nail in a few minutes. Figure B What You Saw (Observations) The nail is coated with copper., This is the equation for the. I Fe + CuS FeS0 4 + Cu Iron Copper sulfate Iron sulfate Copper I 1. Name the free element we started with. _ 2. Name the compound we started with Name the free element we ended with. _ 4. Name the compound we ended with. _ 5. a) Which element did the iron replace? _ b) What happened to this element? _ 6. What do we call this kind of chemical? _ 7. What happens during a single replacement? _ 99

4 IDENTIFYING SINGLE REPLACEMENT REACTIONS Six equations are listed below. Some are single replacement (V') in the correct box next to each equation. s. Some are not. Mark a check Single Not a single Equation replacement replacement 1. C + 2S CS 2 2. H H AI + 6HCI 2AICl 3 + 3H K + Cl 2 2KCl - 5. Zn + PbO ZnO + Pb 6. Fe + CuS0 4 FeS0 4 + Cu DOUBLE REPLACEMENT REACTIONS A single replacement takes place between an element and a compound. The free element replaces one of the elements of the compound. This produces a new compound and a new free element. A free element + BC compound AC new compound + B new free element A double replacement takes place between two compounds. A part of one compound changes place with a part of the other compound. Let us use playing children as models again to see what happens. Children A and B stand for compound AB. Children C and D stand for compound CD. Child A changes place with child C. What do we have now? Instead of compounds AB and CD, we have two new compounds- CB and AD. When there are two change overs, a double replacement has taken place.!aa~i Figure C Figure D AIt]l~ c"1n( Figure E 100

5 Now let us study an actual double replacement -the hydroxide (NaOH), and hydrochloric acid (HCl). between sodium I NaOH + HCI + I The sodium and hydrogen change places. Two new compounds form-nacl :> NaCI + HOH (common table salt) and HOH (water). Now you try. Read each equation carefully. Then answer the questions or fill in the blanks with each. Equation I BaC1 2 + Barium chloride Na 2 S0 4 Sodium sulfate BaS NaCI Barium sulfate Sodium chloride 1. Name the reactants. 2. The reactants are _ 3. The barium changed places with the _ sulfate, chlorine, sodium 4. Name the products. _ 5. The products are ~~-- :--: --:: -- : What kind of chemical is this? _ 7. Double replacement is the of two to form two new Equation II AgN03 Silver nitrate + NaBr AgBr + Sodium bromide Silver bromide NaN0 3 Sodium nitrate 8. Name the reactants. 9. The reactants are _ 10. The silver changed places with the sulfate, chlorine, sodium 11. Name the products. 12. The products are _ 13. What kind of chemical is this? _ 101

6 IDENTIFYING DOUBLE REPLACEMENT REACTIONS Eight equations are listed below. Some are double replacement s. Some are not. Mark a check (11') in the correct box next to each equation. Double Not a double Equation replacement replacement 1. Mg(OH)2 + 2HCl -+ MgCl 2 +2HOH 2. C 6 H 10 0 S + H 2 O -+ C 6 H Na 2 S0 4 + BaCl NaCl + BaS Mg + N2 -+ Mg3N2 5. H 2 S0 4 + BaCl HCl + BaS ZnC ZnO + CO 2 7. CuS0 4 + H 2 S -+ H 2 S0 4 + CuS 8. NH 4 N H N 2 0 IDENTIFYING CHEMICAL REACTIONS Ten chemical equations are listed below. Identify each kind of : synthesis, decomposition, single replacement, or double replacement. Equation Kind of 1. N2 + 3H2 -+ 2NH3 2. 2Br2 + 2H2O -+ 4HBr Mg + 2HCl -+ MgCl2 + H2 4. 2KBr + H 2 SO 4 -+ KzS04 + 2HBr 5. H 2 S H20 + S02 6. Na 2 S + 2HCl -+ 2NaCl + H 2 S 7. 2Na + Iz -+ 2NaI 8. NaCl + AgN03 -+ NaN0 3 + AgCl 9. H 2 + Cl HCl 10. H 2 C H CO 2 102