ABSTRAKPenelitian ini bertujuan untuk meningkatkan: (1) Interaksi sosial siswapada materi pokok Kelarutan dan Hasil Kali Kelarutan di SMA Muhammadiyah 1Karanganyar dengan menerapkan model pembelajaran Problem Based Learning(PBL). (2) Prestasi belajar siswa pada materi pokok Kelarutan dan Hasil KaliKelarutan di SMA Muhammadiyah 1 Karanganyar dengan menerapkan modelpembelajaran Problem Based Learning (PBL).Penelitian ini merupakan Penelitian Tindakan Kelas (PTK) yangdilaksanakan dalam dua siklus. Pada setiap siklusnya terdapat empat tahapan yangterdiri dari perencanaan tindakan, pelaksanaan tindakan, observasi, dan refleksi.Subjek penelitian adalah siswa kelas XI.IPA.ICT 1 SMA Muhammadiyah 1Karanganyar tahun pelajaran 2014/2015. Sumber data adalah siswa dan guru.Teknik pengumpulan data melalui observasi, wawancara, kajian dokumen, angket,dan tes. Teknik analisis yang digunakan dalam penelitian ini adalah deskriptifkualitatif.Berdasarkan hasil penelitian dapat disimpulkan bahwa: (1) Penerapanmodel pembelajaran Problem Based Learning (PBL) dapat meningkatkaninteraksi sosial siswa pada materi pokok Kelarutan dan Hasil Kali Kelarutan siswakelas XI.IPA.ICT 1 SMA Muhammadiyah 1 Karanganyar. Hal ini ditunjukkandari peningkatan persentase ketercapaian interaksi sosial siswa yaitu pada siklus Isebesar 79,31% dan pada siklus II sebesar 86,21%. (2) Penerapan modelpembelajaran Problem Based Learning (PBL) dapat meningkatkan prestasi belajarsiswa pada materi pokok Kelarutan dan Hasil Kali Kelarutan siswa kelasXI.IPA.ICT 1 SMA Muhammadiyah 1 Karanganyar. Hal ini dapat dilihat dariprestasi belajar siswa yaitu aspek kognitif dan aspek afektif yang meningkat padasiklus I dan siklus II. Pada siklus I ketercapaian aspek kognitif sebesar 65,52%dan pada siklus II sebesar 82,76%. Ketercapaian aspek afektif pada siklus Isebesar 96,55% dan pada siklus II sebesar 100%. Sedangkan untuk aspekpsikomotor hanya dilakukan pada siklus I dengan persentase ketercapaian sebesar100%.Kata Kunci : penelitian tindakan kelas, problem based learning, interaksi sosial,prestasi belajar, kelarutan dan hasil kali kelarutanABSTRACTThe aims of this research were to improve: (1) Student’s social interactionin the subject matter of Solubility and Solubility Product in SMA Muhammadiyah1 Karanganyar by implementing Problem Based Learning (PBL) model. (2)Student’s learning achievement in the subject matter of Solubility and SolubilityProduct in SMA Muhammadiyah 1 Karanganyar by implementing Problem BasedLearning (PBL) model.This research was a Classroom Action Research (CAR), which wasconsists of two cycles. Every cycle consists of four steps there were planning,acting, observing, and reflecting. The subjects were students of class XI.IPA.ICT1 in SMA Muhammadiyah 1 Karanganyar academic year 2014/2015. Source ofdata were students and teachers. The data collection technique were observations,interviews, document, questionnaires, and test. Analysis of data using qualitativedescriptive method.The result of the research showed that: (1) Implementation of ProblemBased Learning (PBL) model could be improved the student’s social interaction inthe subject matter of Solubility and Solubility Product at class XI.IPA.ICT 1 SMAMuhammadiyah 1 Karanganyar. It can be seen from cycle I the percentage ofstudent’s social interaction was 79.31% and increased to 86.21% in the cycle II.(2) Implementation of Problem Based Learning (PBL) model could be improvedthe student’s learning achievement in the subject matter of Solubility andSolubility Product at class XI.IPA.ICT 1 SMA Muhammadiyah 1 Karanganyar. Itcan be seen from increased of student’s learning achievement which was includedtwo aspect such as cognitive and affective aspects. Cognitive aspectsimprovement from 65.52% in cycle I to 82.76% in cycle II. Affective aspectsimprovement from 96.55% in cycle I to 100% in cycle II. Psychomotor aspectsonly performed in cycle I with the achievement percentage of 100%.Keywords : classroom action research, problem based learning, socialinteraction, learning achievement, solubility and solubilityproduct