Questions asked by KPaukstis

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• Why is FeCl3 the product, when Fe and Cl2 reacts and not FeCl2?
  
• How to balance #Zn + HNO_3 -> Zn(NO_3)_2 + NH_4NO_3 + H_2O#?
  
• If my dad has the AB blood group, my mom has the O blood group. What blood group will I be? A, B or AB?
  
• What are the differences between oxidation numbers and ionic charge? Do I have to write e.g #Al^(3+)# or #Al^(+3)#?
  
• How do you know, if the atom will have an alpha, beta or gamma radioactive decay?
  
• What is the Archimedes' principle?
  
• Are radioactive ions a thing?
  
• Is crystal growth a chemical or physical process?
  
• Can metals be in a gaseous state?
  
• Dad and son both work a certain job that they finish in 12days. After 8days the son gets sick. To finish the job dad has to work 5 more days. How many days would they have to work to finish the job, if they work separately?
  
• Tourist covered 600km. Every day he would go the same number of kilometers. If the tourist went 10km more every day, then he would travel for 5 days less. How many days did the tourist travel?
  
• What determines if in a reaction between sodium chloride and sulfuric acid you will get sodium bisulfate or sodium sulfate?
  
• What is the difference between weak acids and strong acids?
  
• For phosphoric fertilizer we calculate the part of the weigh of P2O5 and potassium weight of K2O. We know that 1 ha uses 154kg of this fertilizer (N + P2O5 + K2O in ratio 3:1:3). Let's say we use ammonium nitrate, superphosphate and potassium chloride?
  
• Water fills the tub in 12mins, and empties the tub in 20min when the lid is open. How long will it take to fill an empty tub if the lid is open? Answer: 30min. How do I solve it?
  
• Deers and roes live in the forest. Deers make up 30% of the forest life. There are 144 deers less than roes. How many roes live in the forest? Answer: 252 roes. How do I solve this problem?
  
• The mixture of Na2CO3 and NaHCO3 weighs 220g. Heated precipitate weighs 182g. What is the percent composition?
  
• A cheetah was chasing and antelope which is 700m away. How many minutes will it take the cheetah, which is running at a constant speed of 110km/h to reach the antelope that is running at a constant speed of 75km/h?
  
• The pool is filled using two tubes in 2h. The first tube fills the pool 3h faster than the second tube. How many hours will it take to fill the tube using only the second tube?
  
• Two brigades had to build a house. The first brigade works alone and builds the house in 15days. The second brigade builds it in 30days. How long will it take to build the house when both brigades work together?
  
• Average weight of 5 boys is 65kg, average weight of 4 girls is 56kg. What is the average weight of all 9 kids?
  
• A drink is made by mixing 4 parts of syrup with 9 parts of water. If we have 947,6L of syrup, what much litres of this drink can we make?
  
• A drink is made by mixing 4 parts of syrup with 9 parts of water. If we have 947,6L of syrup, what much litres of this drink can we make?
  
• Why isn't there a compound with the formula FeI3 (ferric iodide)?
  
• A boy was going home for 12km. We went 2km/h faster than last time and now spent 1 hour less on the road. How fast was the boy going?
  
• Anna and Becky have to do a job. Anna would finish the job in 6h if she worked alone. How many hours would it take Becky to do this job, if when working together this works is finished in 4hours?
  
• Item A costs 15% more than item B. Item B costs 0.5€ more then item C. All 3 items (A, B and C) together cost 5.8€. How much does item A cost?
  
• Train A got from one city to another 45min faster than train B. Train's A speed is 48km/h, train's B speed is 36km/h. What is the distance between the cities?
  
• The hall had 160 seats. After the reconstruction every row had one seat added to it, and the number of rows doubled. How many seats were before and after the reconstruction, if the number of seats increased by 38?
  
• There were 110 books in two bookshelves. If we put half of the books from bookshelf B to bookshelf A, then there will be four times more books in bookshelf A, than there is now in bookshelf B. How many books were in the bookshelves in the beginning?
  
• The hall had 160 seats. After the reconstruction every row had one seat added to them, and the number of rows doubled. How many seats were before and after the reconstruction, if the number of seats increased by 38?
  
• Limewater is used to find out if #"CO"_2# is present. How much (in grams) of limestone, that contains 95% calcium carbonate will we need to get 80g 7% of limewater?
  
• Coal is made of 82,2% carbon, 4,6% hydrogen, 1% sulphur and the rest is incombustible. We know that 21% of air is oxygen. Calculate what volume of air will we need to burn 1 tone of this coal?
  
• One tube fills the pool in 15 hours. How many hours and minutes will it take to fill the pool with 4 same type tubes?
  
• What kind of salt (acidic or basic) is #Zn(CH_3COO)_2# solution?
  
• 40 species of animals live in the forest: 7 species more carnivores than ungulates, and 2 species more rodents that carnivores. How many ungulates live in the forest?
  
• Why does copper have a more common oxidation state of +2, but only one valence electron?
  
• Is there a difference between writing f(x), g(x), h(x)? Do the letters f, g, h, etc. have any significance?
  
• 20g of NaCl were added to an 8% 180g of NaCl solution. What is the mass percent of NaCl in the solution now?
  
• Molar mass of substance A in material Eu(A)3 is 238g/mol. 0.476g of substance A was burned and produced 1.408g of CO2 and 0.252g of H2O. Substance A is made up of carbon, hydrogen and oxygen. What is the chemical formula for substance A?
  
• Which of these molecules have the strongest ionic bond? KI, KBr, RbCl, RbF?
  
• 3 moles of sodium reacted with 3 moles of chlorine gas. How much material was left unreacted? How many moles of sodium chloride were produced?
  
• What determines the strength in ionic bonds?
  
• How to obtain phthalic acid from aspirin?
  
• In oxide X2O7 element X has the highest oxidation state. This element in a compound with hydrogen makes up 99.219%. What is this element?
  
• Is methanol a polar molecule?
  
• A piece of iron was placed in a silver nitrate solution. After the reaction iron's mass increased by 3.52g. How many moles of #"Fe"("NO"_3)_2# were produced?
  
• If I had to write down the oxidation states of iron (II) and sulphate ions, should I write them as +2 and -2 or 2+ and 2-?
  
• What is the difference betweet molecular mass (Mr) and molar mass (M)?
  
• How to convert a carboxylic acid to an alcohol?
  
• How can some manganese oxides be acidic and some basic?
  
• After burning 6.08g of silicon and carbon mixture, 8.4g of solid product was produced. The gaseous product was let through a 100mL 15% NaOH solution (density = 1.1g/cm^3). What was the silicon and carbon composition in grams?
  
• After burning 1.5g of some gas, 4.4g of CO2 and 2.7g of H2O were produced. What is this gas if at STP 1L of this gas weighs 1.34g?
  
• Hydrocarbon contains 18.18% hydrogen and 81.82% carbon. One litre of this gas has the same mass as carbon dioxide. What is the molecular formula of this hydrocarbon?
  
• A hydrocarbon contains a benzene ring. It is made up of 91.43% carbon and its molar mass is about 105g/mol. What is the molecular formula of this hydrocarbon?
  
• Can you help me balance this equation? As2S3 + K2Cr2O7 + H2SO4 = H3AsO4 + K2SO4 + Cr2(SO4)3 + H2O + SO2
  
• At #25^@ "C"#, for the reaction #"N"_2"O"_4(g) rightleftharpoons 2"NO"_2(g)#, the equilibrium constant is #K_c = 5.85xx10^(-3)#. #"20.0 g"# of #"N"_2"O"_4# were added to a #"5.00-L"# container. What is the molar concentration of #"NO"_2# at equilibrium?
  
• In meiosis II anaphase we have two cells, each containing 23 chromosomes. After they split, the chromosomes come apart into 23 chromatids in each cell. How do these chromatids replicate themselves into 23 chromosomes if they have crossed-over their genes?
  
• 4.6g of an organic gaseous compound was burned. Its gas density compared to air is 23. After burning this compound, 4.48 L of CO2 (at 0 °C and 1 atm) and 5.4 g of H2O were produced. What is the name and chemical formula of this organic compound?
  
• Gas, that was produced after burning 14.2g of methanol and ethanol mixture were let through lime water. 50g of precipitated out. What is the mass percent of methanol in the mixture?
  
• What volume of methanol (ρ=0.8g/cm^3) needs to be oxidized to produce 500mL 40% formaldehyde (ρ=1.11g/cm^3)?
  
• Object A costs 70% more than object B and 36% more than object C. By how many percent is object B cheaper and object C?
  
• Could you help me figure out what sort of laboratory glassware apparatus this is?
  
• How to prove that x*y*z=1 if a^x=b, b^y=c, c^z=a and a>0, b>0, c>0 and none of them can equal 1?
  
• On the first day the bakery made 200 buns. Every other day the bakery made 5 buns more than the last day and this went up until the bakery made 1695 buns in one day. How many buns did the bakery make in total?
  
• If cos(α)=4/5 and we know that α∈(270˚; 360˚), how much is cos(α/2)?
  
• How many positive numbers can be made from the digits 1, 2, 3, 4, 5, 6, 7, 8 and 9 so that they are smaller than 800? The digits can repeat.
  
• With what integer a is the the graph #y=4x-2# the tangent line of #y=ax^2+28x+14#?
  
• When reacting an acyl chloride with methanol, the chloride leaving group leaves, but later acts as a base? why? Isn't chloride only a nucleophile?
  
• A boat going in the river downstream went 30km in 2 hours. The same boat going upstream reaches the same distance after 6 hours. The river flow speed and the boat's speed are constant throughout the whole journey. What is the river flow speed?
  
• How to calculate the sum (1+2)+(2+3)+(3+4)+...(2012+2013)+(2013+2014)?
  
• Right triangle has a hypotenuse with length 41 cm. The area of the triangle is 180 cm^2. What are the triangle leg lengths?
  
• The sequence a1, a2, a3... an is an arithmetic sequence. a4=-a6. What is a5?
  
• How do I prove that 4sin(62.5˚+x/2)*cos(27.5˚-x/2) is the same as 4sin^2(x/2+62.5˚)?