Search

Waste cooking oil has the potential to be a raw material for biodiesel. The use of heterogeneous catalysts and ultrasonicator will optimize the transesterification and environmentally friendly. Transesterification study of waste cooking oil with SrO-KF nano catalyst has been carried out. This researchs were: refinement of waste cooking oil, synthesis of SrO-KF nano-catalyst, and the transesterification. The catalyst applied ratio of 1:1, 1:2, and 1:3 of SrO:KF with concentrations of 2%, 3% and 4% by weight of oil respectively. The results of heterogeneous catalyst using XRD and SEM showed that SrF2, SrO and KF compounds had been formed. The optimum transesterification conditions were obtained on SrO-KF catalyst (1:2), concentration of 4% (w/w) with a yield of 84.4% (w/w). The methyl ester of waste cooking oil has density of 884 kg/m3, acid number of 0.48 mg/g, and viscosity of 4.2 cSt. Methyl esters of waste cooking oil were composed of 25.14% methyl palmitate and 33.65% methyl elaidate, 11.27% methyl linoleate, 10.14% methyl lauric and a mixture of methyl esters from waste cooking oil has the potential to be used as biodiesel.

Problem-solving is one of the abilities that a student must-have in the 21st century. This is because students' ability to solve problems is expected to increase their competence of higher-order thinking skills (HOTS). Problem-solving ability can be improved in several ways for example, the use of a certain instructional model, worksheets, and assessment or assessment based on problem-solving. This study aimed to develop and implement structured problem-solving assessment with the IDEAL model on acid-base materials, salt hydrolysis, buffer solutions, and acid-base titrations to examine students' problem-solving abilities. The instrument development model used adapts the ADDIE model with four steps, namely analysis, planning, development, and implementation. The research sample were 34 high school students in grade 11 in Sidoarjo, East Java. The result is that the problem-solving ability with the lowest percentage are in the acid-base titration material for the Act on strategy indicator at 27.21%, while the highest percentage of skills are found in the buffer solution material for the Explore solution indicator at 89.5%. This study implies that the test instrument for further research is to measure students' ability to solve structured problems with the IDEAL model on acid and base. This study implies that the test instrument for further research measures students' ability to solve structured problems with the IDEAL model on acid-base, salt hydrolysis, buffer solution, and acid titration. So that the problem solving process with the integration of problem solving problems can improve students' critical thinking.