Ch: #11 - Acids and Bases Flashcards
What do you use when calculating the product made?
(limiting reagent or excess reagent)
The limiting reagent.
What is the defenition of an acid?
Sunbstances that produce H+ ions.
What happens when acids are in a solution?
When acids are dissolved they produce a pH of <7.
What chemicals are common acids?
- HCl (hydrochloric acid)
- H2SO4 (sulfuric acid)
- HNO3 (nitric acid)
- H3PO4 (phosphoric acid)
- non-metal oxides
What is special about non-metal oxides?
They only produce H+ ions in water.
What are the different ways H and Cl atoms can bond? When does it bond this specific way? Is it an acid, base or neutral?
- Covalent
* solid, liquid, gas
* neutral - Ionic
* aqueouse
* acid
What is essential for all acids?
Water
What is a base?
Substances that react with acids to form water.
Most bases produce OH- ions in water
What are bases?
- metal oxides
- metal hydroxides
- metal carbonate
What is alkali?
A base which dissolves in water these are group 1 metal hydroxides/carbonates The pH >7 if the base dissolves.
What is neutralisation?
acid + base react to form water.
What is this reaction called and why?
HCl + NaOH => H2O + NaCl
It is called a proton transfer because the H+ only has 1 proton and no neutrons or electrons. The H+ ion transfers to the oxygen.
The H+ ion bonds with the OH- ion
What happens to the pH in a neutralisation reaction?
The pH moves closer to 7, it will only reach 7 if the acid and base are mixed in equal molar (ratios) quantities.
What is concentration?
Concentration measures the moles of a substance dissolved in a specific volume of solvent (water).
What is the unit for concentration?
mol/dm^3
1dm^3 = 1000cm^3
What color does an acid go in U.I?
U.I. = red
What color does a base go in U.I?
U.I. = blue/purple
What color a neutral substance go in U.I?
U.I. = green
How do you calculate concentration?
Practice on a worksheet
Can any acid have any conc.?
Yes
The concentration of an acid is a measure of what?
The concentration of an acid is a measure of the no. of moles dissolve in a solvent.
Is the concentration or strength of a substance a inherent property?
The strength a a substance is an inherent (fixed) property.
What does the strength of a substance measure?
The degree of dissosiation / ionisation of an acid.
When a strong acid is dissolved describe what happens in terms of ions
All of the ions in the acid are dissociated
Degree of dissosiation = 100%
When a weak acid is dissolved describe what happens in terms of ions
Much of the acid remains together. The degree of dissosiation is much less.
What happens during conduction in HCl?
During conduction, ions are used up and replaced by undissociated molecules.
What is titration?
The method used to accuratley meassure the concentration of a solution.
What is a pipette, how does it look, and when is it used in titration?
What is a burret, how does it look, and when is it used in titration?
What is the aim of titration?
To measure the concentration of the unknown chemical my using titration.
What is the meathod for titration?
- Clean pipette with water
- Clean pipette with intended solution
- Measure 25.000cm^3 of uknown chemical into the pipette.
- Add 2 drops of indicator
- Clean burret with water and make sure tap is closed
- Clean the burret with intended solution (also clean tap)
- Fill burret with HCl and write down initial reading
- Add known chemical (HCl) a bit a a time until it goes colorless (neutral) and identify titre
- Write down a final reading
- Repeat until you have concordant results.
How does the burret measure things?
By how much is added into the chonical flask before
Why is universal indicator not used in titration?
Because it has infinate different colors and is very subjective. It is not completely clear to see when the solution has turned “green”.
How does the table for titration look and what are the rules?
What is the defenition of salts?
Ionic compound formed in a reaction with an acid.
e.g. :
halides
nitrates
sulfates
phosphates
What pH do salts generally have?
Neutral (pH 7)
What are the proporties of salts?
- High mpt. => strong electrostatic forces
- Conduct electricity as (l) and (aq), the ions can move and carry charge
- Soluble in water (exceptions)
Why do some salts dissociate and others don’t?
Because, some salts have lower or higher charges so the solvent can or can’t break the electrostatic forces.
What are the solubility rules? (differentiate the most important rules to the ordinary ones).
- All compounds of group 1 are soluble
- All nitrates are soluble
- All halides are soluble except if they also contain Ag+ or Pb^2+
- All sulfates are soluble except if they also contain Ca^2+, Sr^2+, Ba^2+, Pb^2+
- All hydroxides are insoluble
- All oxides are insoluble , but group 1 metals react with water.
What is the defenition of precipitation
Reaction of two solutions (soluble chemicals) to form a solid.
What are the impurities of filtering the products for precipitation?
The solid (residue) contains two impurities:
1. Water
2. Soluble impurites
What is the method for precipitation (to collect the salt)?
a) Filter the mixture
-Water (impurity)
-Soluble reactants (impurity)
b) Wash residue with distilled water (to dissolve the soluble impurities even more).
c) Evaporate water on hot plate
What are the steps for making ionic equations?
i) Write a symbol equation
ii) Add state symbols
iii) Identify ionic compounds that are (aq)
iv) Seperate those compounds into ions
v) Cancle out left/right
acid + metalcarbonate =>
salt + water + carbon dioxide
What are the three methods for salt preperation?
- Insoluble base
- Titration
- Precipitation
What are the rules for Insoluble base salt preperation?
The salt produced needs to be isolated (pure) and therefor the base used needs to be isoluble so it doesn’t dissolve (all bases are insoluble except if your usinf group 1 metals).
What extra step do you need to do when making salts with insoluble bases using metal oxides/hydroxides
you need to heat metal oxides/hydroxides because they react slowly so they need to be heated to speed up the reaction. Metal carbonates already react quickly.
How do you measure the chemicals for preparing salts with an insoluble base?
It is impossiblet to measure the reactants in perfect equal quantities, one of the reactants will always be in excess. This chemical must be the base becuse if you have excess acid it will be difficult to seperate as it is an (aq) like the salt. While if you have excess base, it is easy to seperate from the salt and water as it is a (s).
What are the 3 different types of mole calculations?
- Mass
- Concentration
- Gas
What is the method for making salts with an insoluble base?
- Measure xcm^3 of acid into a chonical flask
- Add excess base (if it is a carbonate: wait until it stops effervescing
if it is an oxide: Wait until solid no longer disapears (must be heated)) - Filter to remove excess base (residue = base, filtrate = salt+water)
- Heat filtrate in evaporating basin until 3/4 of water has evaporated or until crystals begin to form
- Leave to crystalize
- Filter to remove excess water
- collect residue
Why do you leave some water in evaporation?
- To form large crystals
- To avoid salt decomposing
- To form hydrated crystals
What is the problem with using precipitation to form group 1 salts?
- Detremining excess base is difficult because the base dissolves
- There is no way to seperate the dissolved base from the salt
What method is used to make group 1 salts?
Titration
What is the method for using titration as a salt preperation method?
- Measure 25.00cm^3 of base using into a chonical flask using a pipette
- Add 2 drops of idicator
- Fill burret with acid and record the initial volume
- Add acid to base (slowly) until it turns neutral (color of indicator using)
- Repeate steps 1-4 (without indicator, directly addd 25 cm of base and found volume of acid.
- heat solutions in evaporating basin until crystals start to form
- Levae to crystallize
- Filter to remove excess water
What color does a neutral substance go in phenolphthalein?
Phenolphthalein = colorless
What color is methyl orange in a neutral substance?
Yellow
What color does phenolphthalein go in a basic substance?
Pink
What color does methyl orange go in a basic substance?
yellow
What color does phenolphthalein go in an acidic substance?
Colorless
Whay color does methyl orange go in an acidic substance?
Red/orange
