Un flacon, contenant une solution aqueuse d'un composé qu'on...

Un flacon, contenant une solution aqueuse d'un composé qu'on appellera A, a perdu son étiquette. On peut faire les observations suivantes : > La solution obtenue en mélangeant $50 \mathrm{~mL}$ de $\mathrm{HCl} 0,1 \mathrm{M}$ et $50 \mathrm{~mL}$ de la solution de A présente un $\mathrm{pH}$ de 1,3. La solution obtenue en mélangeant $50 \mathrm{~mL}$ de soude $0,1 \mathrm{M}$ et $50 \mathrm{~mL}$ de la solution de A présente un $\mathrm{pH}$ de 9. Ces résultats permettent-ils de savoir si A est un acide ou une base, fort(e) ou faible, ou un composé indifférent (neutre)?

Un flacon, contenant une solution aqueuse d'un composé qu'on appellera A, a perdu son étiquette. On peut faire les observations suivantes :
> La solution obtenue en mélangeant $50 \mathrm{~mL}$ de $\mathrm{HCl} 0,1 \mathrm{M}$ et $50 \mathrm{~mL}$ de la solution de A présente un $\mathrm{pH}$ de 1,3.
La solution obtenue en mélangeant $50 \mathrm{~mL}$ de soude $0,1 \mathrm{M}$ et $50 \mathrm{~mL}$ de la solution de A présente un $\mathrm{pH}$ de 9.

Ces résultats permettent-ils de savoir si A est un acide ou une base, fort(e) ou faible, ou un composé indifférent (neutre)?

Key Concepts

Strength of Acids and Bases

Acid and base strength is determined by the degree of ionization in water. Strong acids and bases dissociate completely, whereas weak acids and bases only partially dissociate. This concept is vital in interpreting the extent of neutralization during titrations and in predicting the resultant pH of mixtures.

Reactivity in Acidic and Basic Media

Understanding the reactivity of substances in acidic or basic media is essential for identifying their chemical nature. An acid will not react with another acid, and similarly, a base will not react with another base, but a weak acid can react with a strong base to form a conjugate base, affecting the pH of the resulting solution. Such observations help determine whether an unknown compound behaves as an acid, base, or is neutral.

Acid–Base Neutralization

Acid–base neutralization is a reaction where an acid and a base react to form water and a salt. By mixing a known strong acid or base with an unknown solution, one can observe the resulting pH and deduce whether any neutralization has occurred, which helps in identifying the chemical nature of the unknown compound.

pH and Its Significance

The pH scale is a logarithmic measure of the hydrogen ion concentration in a solution, indicating its acidity or basicity. Low pH values correspond to high acidity, while high pH values are indicative of basicity. Observing changes in pH when mixing known reagents provides crucial clues about the reactive properties of an unknown solution.

Transcript

00:01 We are asked to evaluate two chemical reactions, neutralization reactions, and decide if the resulting solution is acidic, basic, or neutral.

00:11 We have two reactions to do.

00:13 The first reaction will be between perchloric acid and sodium hydroxide.

00:28 Our products will be, excuse me, sodium perchlorate and liquid water.

00:45 This should all be balanced.

00:46 We are also given that we have 65 milliliters, which will be 0 .0650 liters of 0 .050 molar acid, and we have 40 milliliters of 0 .0750 molar base.

01:22 Okay.

01:24 So we're, if we have more molds of acid, it'll be acidic.

01:28 More moles of base, it will be basic, and if it's the same moles of each, it will be neutral.

01:35 So let's go and figure out how many bases.

01:38 These are our one -to -one ratios, so we don't have to worry about ratios.

01:44 So we will use our molerities to figure out how many moles of each we have.

01:52 Let's calculate the moles of our acid first.

02:00 Moles of acid will be equal to the volume of the acid in leading.

02:07 Times the concentration, which is moles per liter molarity, and that equals 0 .00325 moles of perchloric acid.

02:34 Our moles of base will equal our milliliters, turn to liters, 0 .0750.

03:05 This will be acidic, this is greater.

03:08 So our concentration of our h plus is greater than our concentration of our oh minus.

03:19 So this is acidic.

03:25 Our second reaction is between nitric acid and calcium hydroxide.

03:41 It would be a little bit more complicated, not much, because we don't have one -to -one more ratios...

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