Answer:
Explanation:
Sodium fluoride, being a salt, dissolves in water completely producing F ⁻ ions. Now F⁻ is the conjugate base of the weak acid HF, so in water we will have the following equilibrium:
F⁻ + H₂O ⇆ HF + OH⁻
Given this equilibrium, we need to calculate Kb from the Ka for HF, the [ OH ⁻] from the given pH, and finally the mass needed to produce that OH⁻ concentration.
The equilibrium constant, Kb , can be calculated from Kw = Ka x Kb, where Kw = 10⁻¹⁴ and Ka for HF is 6.6 x 10⁻⁴ from reference tables.
Kb = 10⁻¹⁴ / 6.6 x 10⁻⁴ = 1.5 x 10⁻¹¹
pH + pOH = 14 ⇒ pOH = 14 - 8.40 = 5.60
[ OH⁻ ] = 10^-5.60 = 2.51 x 10⁻⁶
Now we have all the information :
F⁻ HF OH⁻
Equilibrium X 2.51 x 10⁻⁶ 2.51 x 10⁻⁶
(2.51 x 10⁻⁶)² / X = 1.5 x 10⁻¹¹ ⇒ X = (2.51 x 10⁻⁶)² / 1.5 x 10⁻¹¹
X = [ F⁻ ] = 0.41 M
For 350 mL ( 0.35 L ) we need to add:
0.41 mol HF/ 1 L * 0.35 L = 0.144 mol
and finally the mass will be:
0.144 mol NaF * 42.0 g/mol NaF = 6.03 g NaF
The s-, p-, and d-block elements of the periodic table are arranged into 18 numbered columns, or groups. The elements in each group have the same number of valence electrons. As a result, elements in the same group often display similar properties and reactivity.
I’m pretty sure it’s 7.5 (7 and a half hours) sorry if i’m wrong
You can do this by dividing by the molar mass of Zn:
Steel Wool + Oxygen (Fire) The steel wool is a grayish color and has a rough surface. Oxygen is transparent It looks like a powder, and like if it was rusted steel wool but then broken apart and turned into a powder Well Iron oxide is 7 grams and steel wool combined is 7 grams so you can say that the mass was conserved Yes, this is a chemical change because the steel wool rusted and rust is a chemical change, so iron oxide is cause because if a physical change.
Egg + Heat The egg has a yellow yolk in the middle while there is some type of liquid at the border of the yolk, but it is clear, the heat is hot but transparent The egg turned into a delicious food called an omelet what was yolk staid as a liquid but got a tad harder, but the transparent border around it turned white It was conserved because the eggshell was 4 grams and the fried egg is 41 grams It is a chemical change because it results in the formation of new particles, and the chemical bonds break up and new ones are formed.
Water + Heat The water is a clear liquid, while the heat is very hot but transparent The water turned into a type of oxygen -Water Vapor- If 5 g of water becomes a gas it becomes 5 g of water vapor. The mass of the liquid water is simply transferred into the mass of the newly formed water vapor. There was no chemical reaction because the water vapor can be turned back to water also it just changed from a liquid to a gas and did not change its composition
Zinc + Hydrogen Chloride Zinc: a white/silver metallic solid. Hydrogen chloride (dilute hydroelectric acid) a transparent, colorless liquid with a very low pH (acidic). Zinc "dissolved" in hydrogen chloride, while emitting a colorless gas. The liquid remains a colorless liquid, possibly still having a low pH from the unused acid. The colorless gas collected in a test tube gives a popping sound when ignited with a burning wooden splint, so it is not air embedded in the zinc, nor dissolved in hydroelectric acid. Well although the zinc chloride is 12 grams and not 15 the gas that was released was 3 grams and as we all know 3 + 12 is 15 so you could say that the mass was conserved The production of a new substance (most probably hydrogen) from the reaction of the two reactants. When a few drops of the liquid product are evaporated on a watch glass, a white residue is left. When a few drops of the liquid hydroelectric acid are evaporated on a watch glass, there is no residue. This proves that a new product (hydrogen gas), (white powder, zinc chloride) is produced instead of zinc being physically dissolved in hydroelectric acid.
Sodium Hydroxide + Copper Sulfate Sodium hydroxide is a turbid solution and copper sulfate is in form of bright blue crystals. When their solutions are mixed with each other, a pale blue precipitate of basic copper hydroxide & a solution of neutral salt sodium sulfate will be formed. The sodium hydroxide and the copper sulfate combined make a total of 67 grams and the product is split because the sodium sulfate is 47 grams and the copper hydroxide is 20 grams but all together it is still 67 grams so you could say that the mass was conserved The proof of the reaction is the appearance of pale blue precipitates of basic copper hydroxide & a solution of neutral salt sodium sulfate.
