Aprecipitation reaction is caused by mixing 100. ml of 0.25 m k2cr2o7 solution with 100. ml of 0.25 m pb(no3)2 solution. when the precipitate forms, it is filtered from the mixture. which describes the changes in concentration of the spectator ions k+ and no3- in the reaction mixture as the reaction occurs? k+ is doubled, no3- halvedneither is affectedboth are doubledk+ is halved, no3- halved

Both K+ and NO3- concentrations are halved

Explanation:

Since the reaction is

K₂Cr₂O₇ + Pb(NO₃)₂  2K(NO₃) + PbCr₂O₇

knowing that K+ and NO3- are spectator ions, their concentration do not change due to reaction but it will change due to the mixing of volumes of the reactants since we are mixing volumes of different concentrations.

for K+ initially we have:

c K+ initial = 0.25 M  

c K+ final = n/ V = C i * Vin / Vfinal = 0.25 M * 100 ml / 200 ml = 0.125 M

the 200 ml comes from mixing the 100 ml of Pb(NO₃)₂ and 100 ml of K₂Cr₂O₇ ( assuming that the volume of the precipitate is insignificant relative to the solution , it does not occlude a significant portion of the saturated solution and assuming that any volume contraction/expansion due to non ideal behaviour of the solution is negligible)

the same happens with NO3- ,therefore its concentration is also halved

- calcium has greater affinity to bond with electron receptors than hydrogen does and hence, it has the ability to replace hydrogen in most of its compounds.

- lithium has 2 valence electrons in the product because it can make only 1 bond with hydrogen. beryllium has 4 valence electrons in the product because it can only make 2 bonds. it has fewer electrons than neon and can react with electron donors. each hydrogen has 2 valence electrons, the same as helium.

- the covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge.

- a hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine.

so the best choice is a.) 2 calcium (ca) atoms

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.